/*
 * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 */

package java.util;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.lang.reflect.Array;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * This class consists exclusively of static methods that operate on or return
 * collections.  It contains polymorphic algorithms that operate on
 * collections, "wrappers", which return a new collection backed by a
 * specified collection, and a few other odds and ends.
 *
 * <p>The methods of this class all throw a <tt>NullPointerException</tt>
 * if the collections or class objects provided to them are null.
 *
 * <p>The documentation for the polymorphic algorithms contained in this class
 * generally includes a brief description of the <i>implementation</i>.  Such
 * descriptions should be regarded as <i>implementation notes</i>, rather than
 * parts of the <i>specification</i>.  Implementors should feel free to
 * substitute other algorithms, so long as the specification itself is adhered
 * to.  (For example, the algorithm used by <tt>sort</tt> does not have to be
 * a mergesort, but it does have to be <i>stable</i>.)
 *
 * <p>The "destructive" algorithms contained in this class, that is, the
 * algorithms that modify the collection on which they operate, are specified
 * to throw <tt>UnsupportedOperationException</tt> if the collection does not
 * support the appropriate mutation primitive(s), such as the <tt>set</tt>
 * method.  These algorithms may, but are not required to, throw this
 * exception if an invocation would have no effect on the collection.  For
 * example, invoking the <tt>sort</tt> method on an unmodifiable list that is
 * already sorted may or may not throw <tt>UnsupportedOperationException</tt>.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see     Collection
 * @see     Set
 * @see     List
 * @see     Map
 * @since   1.2
 */

public class Collections {
	// Suppresses default constructor, ensuring non-instantiability.
	private Collections() {
	}

	// Algorithms

	/*
	 * Tuning parameters for algorithms - Many of the List algorithms have
	 * two implementations, one of which is appropriate for RandomAccess
	 * lists, the other for "sequential."  Often, the random access variant
	 * yields better performance on small sequential access lists.  The
	 * tuning parameters below determine the cutoff point for what constitutes
	 * a "small" sequential access list for each algorithm.  The values below
	 * were empirically determined to work well for LinkedList. Hopefully
	 * they should be reasonable for other sequential access List
	 * implementations.  Those doing performance work on this code would
	 * do well to validate the values of these parameters from time to time.
	 * (The first word of each tuning parameter name is the algorithm to which
	 * it applies.)
	 */
	private static final int BINARYSEARCH_THRESHOLD   = 5000;
	private static final int REVERSE_THRESHOLD        =   18;
	private static final int SHUFFLE_THRESHOLD        =    5;
	private static final int FILL_THRESHOLD           =   25;
	private static final int ROTATE_THRESHOLD         =  100;
	private static final int COPY_THRESHOLD           =   10;
	private static final int REPLACEALL_THRESHOLD     =   11;
	private static final int INDEXOFSUBLIST_THRESHOLD =   35;

	/**
	 * Sorts the specified list into ascending order, according to the
	 * {@linkplain Comparable natural ordering} of its elements.
	 * All elements in the list must implement the {@link Comparable}
	 * interface.  Furthermore, all elements in the list must be
	 * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)}
	 * must not throw a {@code ClassCastException} for any elements
	 * {@code e1} and {@code e2} in the list).
	 *
	 * <p>This sort is guaranteed to be <i>stable</i>:  equal elements will
	 * not be reordered as a result of the sort.
	 *
	 * <p>The specified list must be modifiable, but need not be resizable.
	 *
	 * @implNote
	 * This implementation defers to the {@link List#sort(Comparator)}
	 * method using the specified list and a {@code null} comparator.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be sorted.
	 * @throws ClassCastException if the list contains elements that are not
	 *         <i>mutually comparable</i> (for example, strings and integers).
	 * @throws UnsupportedOperationException if the specified list's
	 *         list-iterator does not support the {@code set} operation.
	 * @throws IllegalArgumentException (optional) if the implementation
	 *         detects that the natural ordering of the list elements is
	 *         found to violate the {@link Comparable} contract
	 * @see List#sort(Comparator)
	 */
	@SuppressWarnings("unchecked")
	public static <T extends Comparable<? super T>> void sort(List<T> list) {
		list.sort(null);
	}

	/**
	 * Sorts the specified list according to the order induced by the
	 * specified comparator.  All elements in the list must be <i>mutually
	 * comparable</i> using the specified comparator (that is,
	 * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
	 * for any elements {@code e1} and {@code e2} in the list).
	 *
	 * <p>This sort is guaranteed to be <i>stable</i>:  equal elements will
	 * not be reordered as a result of the sort.
	 *
	 * <p>The specified list must be modifiable, but need not be resizable.
	 *
	 * @implNote
	 * This implementation defers to the {@link List#sort(Comparator)}
	 * method using the specified list and comparator.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be sorted.
	 * @param  c the comparator to determine the order of the list.  A
	 *        {@code null} value indicates that the elements' <i>natural
	 *        ordering</i> should be used.
	 * @throws ClassCastException if the list contains elements that are not
	 *         <i>mutually comparable</i> using the specified comparator.
	 * @throws UnsupportedOperationException if the specified list's
	 *         list-iterator does not support the {@code set} operation.
	 * @throws IllegalArgumentException (optional) if the comparator is
	 *         found to violate the {@link Comparator} contract
	 * @see List#sort(Comparator)
	 */
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> void sort(List<T> list, Comparator<? super T> c) {
		list.sort(c);
	}


	/**
	 * Searches the specified list for the specified object using the binary
	 * search algorithm.  The list must be sorted into ascending order
	 * according to the {@linkplain Comparable natural ordering} of its
	 * elements (as by the {@link #sort(List)} method) prior to making this
	 * call.  If it is not sorted, the results are undefined.  If the list
	 * contains multiple elements equal to the specified object, there is no
	 * guarantee which one will be found.
	 *
	 * <p>This method runs in log(n) time for a "random access" list (which
	 * provides near-constant-time positional access).  If the specified list
	 * does not implement the {@link RandomAccess} interface and is large,
	 * this method will do an iterator-based binary search that performs
	 * O(n) link traversals and O(log n) element comparisons.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be searched.
	 * @param  key the key to be searched for.
	 * @return the index of the search key, if it is contained in the list;
	 *         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
	 *         <i>insertion point</i> is defined as the point at which the
	 *         key would be inserted into the list: the index of the first
	 *         element greater than the key, or <tt>list.size()</tt> if all
	 *         elements in the list are less than the specified key.  Note
	 *         that this guarantees that the return value will be &gt;= 0 if
	 *         and only if the key is found.
	 * @throws ClassCastException if the list contains elements that are not
	 *         <i>mutually comparable</i> (for example, strings and
	 *         integers), or the search key is not mutually comparable
	 *         with the elements of the list.
	 */
	public static <T>
	int binarySearch(List<? extends Comparable<? super T>> list, T key) {
		if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
			return Collections.indexedBinarySearch(list, key);
		else
			return Collections.iteratorBinarySearch(list, key);
	}

	private static <T>
	int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) {
		int low = 0;
		int high = list.size()-1;

		while (low <= high) {
			int mid = (low + high) >>> 1;
			Comparable<? super T> midVal = list.get(mid);
			int cmp = midVal.compareTo(key);

			if (cmp < 0)
				low = mid + 1;
			else if (cmp > 0)
				high = mid - 1;
			else
				return mid; // key found
		}
		return -(low + 1);  // key not found
	}

	private static <T>
	int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key)
	{
		int low = 0;
		int high = list.size()-1;
		ListIterator<? extends Comparable<? super T>> i = list.listIterator();

		while (low <= high) {
			int mid = (low + high) >>> 1;
			Comparable<? super T> midVal = get(i, mid);
			int cmp = midVal.compareTo(key);

			if (cmp < 0)
				low = mid + 1;
			else if (cmp > 0)
				high = mid - 1;
			else
				return mid; // key found
		}
		return -(low + 1);  // key not found
	}

	/**
	 * Gets the ith element from the given list by repositioning the specified
	 * list listIterator.
	 */
	private static <T> T get(ListIterator<? extends T> i, int index) {
		T obj = null;
		int pos = i.nextIndex();
		if (pos <= index) {
			do {
				obj = i.next();
			} while (pos++ < index);
		} else {
			do {
				obj = i.previous();
			} while (--pos > index);
		}
		return obj;
	}

	/**
	 * Searches the specified list for the specified object using the binary
	 * search algorithm.  The list must be sorted into ascending order
	 * according to the specified comparator (as by the
	 * {@link #sort(List, Comparator) sort(List, Comparator)}
	 * method), prior to making this call.  If it is
	 * not sorted, the results are undefined.  If the list contains multiple
	 * elements equal to the specified object, there is no guarantee which one
	 * will be found.
	 *
	 * <p>This method runs in log(n) time for a "random access" list (which
	 * provides near-constant-time positional access).  If the specified list
	 * does not implement the {@link RandomAccess} interface and is large,
	 * this method will do an iterator-based binary search that performs
	 * O(n) link traversals and O(log n) element comparisons.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be searched.
	 * @param  key the key to be searched for.
	 * @param  c the comparator by which the list is ordered.
	 *         A <tt>null</tt> value indicates that the elements'
	 *         {@linkplain Comparable natural ordering} should be used.
	 * @return the index of the search key, if it is contained in the list;
	 *         otherwise, <tt>(-(<i>insertion point</i>) - 1)</tt>.  The
	 *         <i>insertion point</i> is defined as the point at which the
	 *         key would be inserted into the list: the index of the first
	 *         element greater than the key, or <tt>list.size()</tt> if all
	 *         elements in the list are less than the specified key.  Note
	 *         that this guarantees that the return value will be &gt;= 0 if
	 *         and only if the key is found.
	 * @throws ClassCastException if the list contains elements that are not
	 *         <i>mutually comparable</i> using the specified comparator,
	 *         or the search key is not mutually comparable with the
	 *         elements of the list using this comparator.
	 */
	@SuppressWarnings("unchecked")
	public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
		if (c==null)
			return binarySearch((List<? extends Comparable<? super T>>) list, key);

		if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
			return Collections.indexedBinarySearch(list, key, c);
		else
			return Collections.iteratorBinarySearch(list, key, c);
	}

	private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
		int low = 0;
		int high = l.size()-1;

		while (low <= high) {
			int mid = (low + high) >>> 1;
			T midVal = l.get(mid);
			int cmp = c.compare(midVal, key);

			if (cmp < 0)
				low = mid + 1;
			else if (cmp > 0)
				high = mid - 1;
			else
				return mid; // key found
		}
		return -(low + 1);  // key not found
	}

	private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
		int low = 0;
		int high = l.size()-1;
		ListIterator<? extends T> i = l.listIterator();

		while (low <= high) {
			int mid = (low + high) >>> 1;
			T midVal = get(i, mid);
			int cmp = c.compare(midVal, key);

			if (cmp < 0)
				low = mid + 1;
			else if (cmp > 0)
				high = mid - 1;
			else
				return mid; // key found
		}
		return -(low + 1);  // key not found
	}

	/**
	 * Reverses the order of the elements in the specified list.<p>
	 *
	 * This method runs in linear time.
	 *
	 * @param  list the list whose elements are to be reversed.
	 * @throws UnsupportedOperationException if the specified list or
	 *         its list-iterator does not support the <tt>set</tt> operation.
	 */
	@SuppressWarnings({"rawtypes", "unchecked"})
	public static void reverse(List<?> list) {
		int size = list.size();
		if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
			for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)
				swap(list, i, j);
		} else {
			// instead of using a raw type here, it's possible to capture
			// the wildcard but it will require a call to a supplementary
			// private method
			ListIterator fwd = list.listIterator();
			ListIterator rev = list.listIterator(size);
			for (int i=0, mid=list.size()>>1; i<mid; i++) {
				Object tmp = fwd.next();
				fwd.set(rev.previous());
				rev.set(tmp);
			}
		}
	}

	/**
	 * Randomly permutes the specified list using a default source of
	 * randomness.  All permutations occur with approximately equal
	 * likelihood.
	 *
	 * <p>The hedge "approximately" is used in the foregoing description because
	 * default source of randomness is only approximately an unbiased source
	 * of independently chosen bits. If it were a perfect source of randomly
	 * chosen bits, then the algorithm would choose permutations with perfect
	 * uniformity.
	 *
	 * <p>This implementation traverses the list backwards, from the last
	 * element up to the second, repeatedly swapping a randomly selected element
	 * into the "current position".  Elements are randomly selected from the
	 * portion of the list that runs from the first element to the current
	 * position, inclusive.
	 *
	 * <p>This method runs in linear time.  If the specified list does not
	 * implement the {@link RandomAccess} interface and is large, this
	 * implementation dumps the specified list into an array before shuffling
	 * it, and dumps the shuffled array back into the list.  This avoids the
	 * quadratic behavior that would result from shuffling a "sequential
	 * access" list in place.
	 *
	 * @param  list the list to be shuffled.
	 * @throws UnsupportedOperationException if the specified list or
	 *         its list-iterator does not support the <tt>set</tt> operation.
	 */
	public static void shuffle(List<?> list) {
		Random rnd = r;
		if (rnd == null)
			r = rnd = new Random(); // harmless race.
		shuffle(list, rnd);
	}

	private static Random r;

	/**
	 * Randomly permute the specified list using the specified source of
	 * randomness.  All permutations occur with equal likelihood
	 * assuming that the source of randomness is fair.<p>
	 *
	 * This implementation traverses the list backwards, from the last element
	 * up to the second, repeatedly swapping a randomly selected element into
	 * the "current position".  Elements are randomly selected from the
	 * portion of the list that runs from the first element to the current
	 * position, inclusive.<p>
	 *
	 * This method runs in linear time.  If the specified list does not
	 * implement the {@link RandomAccess} interface and is large, this
	 * implementation dumps the specified list into an array before shuffling
	 * it, and dumps the shuffled array back into the list.  This avoids the
	 * quadratic behavior that would result from shuffling a "sequential
	 * access" list in place.
	 *
	 * @param  list the list to be shuffled.
	 * @param  rnd the source of randomness to use to shuffle the list.
	 * @throws UnsupportedOperationException if the specified list or its
	 *         list-iterator does not support the <tt>set</tt> operation.
	 */
	@SuppressWarnings({"rawtypes", "unchecked"})
	public static void shuffle(List<?> list, Random rnd) {
		int size = list.size();
		if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
			for (int i=size; i>1; i--)
				swap(list, i-1, rnd.nextInt(i));
		} else {
			Object arr[] = list.toArray();

			// Shuffle array
			for (int i=size; i>1; i--)
				swap(arr, i-1, rnd.nextInt(i));

			// Dump array back into list
			// instead of using a raw type here, it's possible to capture
			// the wildcard but it will require a call to a supplementary
			// private method
			ListIterator it = list.listIterator();
			for (int i=0; i<arr.length; i++) {
				it.next();
				it.set(arr[i]);
			}
		}
	}

	/**
	 * Swaps the elements at the specified positions in the specified list.
	 * (If the specified positions are equal, invoking this method leaves
	 * the list unchanged.)
	 *
	 * @param list The list in which to swap elements.
	 * @param i the index of one element to be swapped.
	 * @param j the index of the other element to be swapped.
	 * @throws IndexOutOfBoundsException if either <tt>i</tt> or <tt>j</tt>
	 *         is out of range (i &lt; 0 || i &gt;= list.size()
	 *         || j &lt; 0 || j &gt;= list.size()).
	 * @since 1.4
	 */
	@SuppressWarnings({"rawtypes", "unchecked"})
	public static void swap(List<?> list, int i, int j) {
		// instead of using a raw type here, it's possible to capture
		// the wildcard but it will require a call to a supplementary
		// private method
		final List l = list;
		l.set(i, l.set(j, l.get(i)));
	}

	/**
	 * Swaps the two specified elements in the specified array.
	 */
	private static void swap(Object[] arr, int i, int j) {
		Object tmp = arr[i];
		arr[i] = arr[j];
		arr[j] = tmp;
	}

	/**
	 * Replaces all of the elements of the specified list with the specified
	 * element. <p>
	 *
	 * This method runs in linear time.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be filled with the specified element.
	 * @param  obj The element with which to fill the specified list.
	 * @throws UnsupportedOperationException if the specified list or its
	 *         list-iterator does not support the <tt>set</tt> operation.
	 */
	public static <T> void fill(List<? super T> list, T obj) {
		int size = list.size();

		if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
			for (int i=0; i<size; i++)
				list.set(i, obj);
		} else {
			ListIterator<? super T> itr = list.listIterator();
			for (int i=0; i<size; i++) {
				itr.next();
				itr.set(obj);
			}
		}
	}

	/**
	 * Copies all of the elements from one list into another.  After the
	 * operation, the index of each copied element in the destination list
	 * will be identical to its index in the source list.  The destination
	 * list must be at least as long as the source list.  If it is longer, the
	 * remaining elements in the destination list are unaffected. <p>
	 *
	 * This method runs in linear time.
	 *
	 * @param  <T> the class of the objects in the lists
	 * @param  dest The destination list.
	 * @param  src The source list.
	 * @throws IndexOutOfBoundsException if the destination list is too small
	 *         to contain the entire source List.
	 * @throws UnsupportedOperationException if the destination list's
	 *         list-iterator does not support the <tt>set</tt> operation.
	 */
	public static <T> void copy(List<? super T> dest, List<? extends T> src) {
		int srcSize = src.size();
		if (srcSize > dest.size())
			throw new IndexOutOfBoundsException("Source does not fit in dest");

		if (srcSize < COPY_THRESHOLD ||
				(src instanceof RandomAccess && dest instanceof RandomAccess)) {
			for (int i=0; i<srcSize; i++)
				dest.set(i, src.get(i));
		} else {
			ListIterator<? super T> di=dest.listIterator();
			ListIterator<? extends T> si=src.listIterator();
			for (int i=0; i<srcSize; i++) {
				di.next();
				di.set(si.next());
			}
		}
	}

	/**
	 * Returns the minimum element of the given collection, according to the
	 * <i>natural ordering</i> of its elements.  All elements in the
	 * collection must implement the <tt>Comparable</tt> interface.
	 * Furthermore, all elements in the collection must be <i>mutually
	 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
	 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
	 * <tt>e2</tt> in the collection).<p>
	 *
	 * This method iterates over the entire collection, hence it requires
	 * time proportional to the size of the collection.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  coll the collection whose minimum element is to be determined.
	 * @return the minimum element of the given collection, according
	 *         to the <i>natural ordering</i> of its elements.
	 * @throws ClassCastException if the collection contains elements that are
	 *         not <i>mutually comparable</i> (for example, strings and
	 *         integers).
	 * @throws NoSuchElementException if the collection is empty.
	 * @see Comparable
	 */
	public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
		Iterator<? extends T> i = coll.iterator();
		T candidate = i.next();

		while (i.hasNext()) {
			T next = i.next();
			if (next.compareTo(candidate) < 0)
				candidate = next;
		}
		return candidate;
	}

	/**
	 * Returns the minimum element of the given collection, according to the
	 * order induced by the specified comparator.  All elements in the
	 * collection must be <i>mutually comparable</i> by the specified
	 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
	 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
	 * <tt>e2</tt> in the collection).<p>
	 *
	 * This method iterates over the entire collection, hence it requires
	 * time proportional to the size of the collection.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  coll the collection whose minimum element is to be determined.
	 * @param  comp the comparator with which to determine the minimum element.
	 *         A <tt>null</tt> value indicates that the elements' <i>natural
	 *         ordering</i> should be used.
	 * @return the minimum element of the given collection, according
	 *         to the specified comparator.
	 * @throws ClassCastException if the collection contains elements that are
	 *         not <i>mutually comparable</i> using the specified comparator.
	 * @throws NoSuchElementException if the collection is empty.
	 * @see Comparable
	 */
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
		if (comp==null)
			return (T)min((Collection) coll);

		Iterator<? extends T> i = coll.iterator();
		T candidate = i.next();

		while (i.hasNext()) {
			T next = i.next();
			if (comp.compare(next, candidate) < 0)
				candidate = next;
		}
		return candidate;
	}

	/**
	 * Returns the maximum element of the given collection, according to the
	 * <i>natural ordering</i> of its elements.  All elements in the
	 * collection must implement the <tt>Comparable</tt> interface.
	 * Furthermore, all elements in the collection must be <i>mutually
	 * comparable</i> (that is, <tt>e1.compareTo(e2)</tt> must not throw a
	 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
	 * <tt>e2</tt> in the collection).<p>
	 *
	 * This method iterates over the entire collection, hence it requires
	 * time proportional to the size of the collection.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  coll the collection whose maximum element is to be determined.
	 * @return the maximum element of the given collection, according
	 *         to the <i>natural ordering</i> of its elements.
	 * @throws ClassCastException if the collection contains elements that are
	 *         not <i>mutually comparable</i> (for example, strings and
	 *         integers).
	 * @throws NoSuchElementException if the collection is empty.
	 * @see Comparable
	 */
	public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
		Iterator<? extends T> i = coll.iterator();
		T candidate = i.next();

		while (i.hasNext()) {
			T next = i.next();
			if (next.compareTo(candidate) > 0)
				candidate = next;
		}
		return candidate;
	}

	/**
	 * Returns the maximum element of the given collection, according to the
	 * order induced by the specified comparator.  All elements in the
	 * collection must be <i>mutually comparable</i> by the specified
	 * comparator (that is, <tt>comp.compare(e1, e2)</tt> must not throw a
	 * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
	 * <tt>e2</tt> in the collection).<p>
	 *
	 * This method iterates over the entire collection, hence it requires
	 * time proportional to the size of the collection.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  coll the collection whose maximum element is to be determined.
	 * @param  comp the comparator with which to determine the maximum element.
	 *         A <tt>null</tt> value indicates that the elements' <i>natural
	 *        ordering</i> should be used.
	 * @return the maximum element of the given collection, according
	 *         to the specified comparator.
	 * @throws ClassCastException if the collection contains elements that are
	 *         not <i>mutually comparable</i> using the specified comparator.
	 * @throws NoSuchElementException if the collection is empty.
	 * @see Comparable
	 */
	@SuppressWarnings({"unchecked", "rawtypes"})
	public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
		if (comp==null)
			return (T)max((Collection) coll);

		Iterator<? extends T> i = coll.iterator();
		T candidate = i.next();

		while (i.hasNext()) {
			T next = i.next();
			if (comp.compare(next, candidate) > 0)
				candidate = next;
		}
		return candidate;
	}

	/**
	 * Rotates the elements in the specified list by the specified distance.
	 * After calling this method, the element at index <tt>i</tt> will be
	 * the element previously at index <tt>(i - distance)</tt> mod
	 * <tt>list.size()</tt>, for all values of <tt>i</tt> between <tt>0</tt>
	 * and <tt>list.size()-1</tt>, inclusive.  (This method has no effect on
	 * the size of the list.)
	 *
	 * <p>For example, suppose <tt>list</tt> comprises<tt> [t, a, n, k, s]</tt>.
	 * After invoking <tt>Collections.rotate(list, 1)</tt> (or
	 * <tt>Collections.rotate(list, -4)</tt>), <tt>list</tt> will comprise
	 * <tt>[s, t, a, n, k]</tt>.
	 *
	 * <p>Note that this method can usefully be applied to sublists to
	 * move one or more elements within a list while preserving the
	 * order of the remaining elements.  For example, the following idiom
	 * moves the element at index <tt>j</tt> forward to position
	 * <tt>k</tt> (which must be greater than or equal to <tt>j</tt>):
	 * <pre>
	 *     Collections.rotate(list.subList(j, k+1), -1);
	 * </pre>
	 * To make this concrete, suppose <tt>list</tt> comprises
	 * <tt>[a, b, c, d, e]</tt>.  To move the element at index <tt>1</tt>
	 * (<tt>b</tt>) forward two positions, perform the following invocation:
	 * <pre>
	 *     Collections.rotate(l.subList(1, 4), -1);
	 * </pre>
	 * The resulting list is <tt>[a, c, d, b, e]</tt>.
	 *
	 * <p>To move more than one element forward, increase the absolute value
	 * of the rotation distance.  To move elements backward, use a positive
	 * shift distance.
	 *
	 * <p>If the specified list is small or implements the {@link
	 * RandomAccess} interface, this implementation exchanges the first
	 * element into the location it should go, and then repeatedly exchanges
	 * the displaced element into the location it should go until a displaced
	 * element is swapped into the first element.  If necessary, the process
	 * is repeated on the second and successive elements, until the rotation
	 * is complete.  If the specified list is large and doesn't implement the
	 * <tt>RandomAccess</tt> interface, this implementation breaks the
	 * list into two sublist views around index <tt>-distance mod size</tt>.
	 * Then the {@link #reverse(List)} method is invoked on each sublist view,
	 * and finally it is invoked on the entire list.  For a more complete
	 * description of both algorithms, see Section 2.3 of Jon Bentley's
	 * <i>Programming Pearls</i> (Addison-Wesley, 1986).
	 *
	 * @param list the list to be rotated.
	 * @param distance the distance to rotate the list.  There are no
	 *        constraints on this value; it may be zero, negative, or
	 *        greater than <tt>list.size()</tt>.
	 * @throws UnsupportedOperationException if the specified list or
	 *         its list-iterator does not support the <tt>set</tt> operation.
	 * @since 1.4
	 */
	public static void rotate(List<?> list, int distance) {
		if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
			rotate1(list, distance);
		else
			rotate2(list, distance);
	}

	private static <T> void rotate1(List<T> list, int distance) {
		int size = list.size();
		if (size == 0)
			return;
		distance = distance % size;
		if (distance < 0)
			distance += size;
		if (distance == 0)
			return;

		for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
			T displaced = list.get(cycleStart);
			int i = cycleStart;
			do {
				i += distance;
				if (i >= size)
					i -= size;
				displaced = list.set(i, displaced);
				nMoved ++;
			} while (i != cycleStart);
		}
	}

	private static void rotate2(List<?> list, int distance) {
		int size = list.size();
		if (size == 0)
			return;
		int mid =  -distance % size;
		if (mid < 0)
			mid += size;
		if (mid == 0)
			return;

		reverse(list.subList(0, mid));
		reverse(list.subList(mid, size));
		reverse(list);
	}

	/**
	 * Replaces all occurrences of one specified value in a list with another.
	 * More formally, replaces with <tt>newVal</tt> each element <tt>e</tt>
	 * in <tt>list</tt> such that
	 * <tt>(oldVal==null ? e==null : oldVal.equals(e))</tt>.
	 * (This method has no effect on the size of the list.)
	 *
	 * @param  <T> the class of the objects in the list
	 * @param list the list in which replacement is to occur.
	 * @param oldVal the old value to be replaced.
	 * @param newVal the new value with which <tt>oldVal</tt> is to be
	 *        replaced.
	 * @return <tt>true</tt> if <tt>list</tt> contained one or more elements
	 *         <tt>e</tt> such that
	 *         <tt>(oldVal==null ?  e==null : oldVal.equals(e))</tt>.
	 * @throws UnsupportedOperationException if the specified list or
	 *         its list-iterator does not support the <tt>set</tt> operation.
	 * @since  1.4
	 */
	public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
		boolean result = false;
		int size = list.size();
		if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
			if (oldVal==null) {
				for (int i=0; i<size; i++) {
					if (list.get(i)==null) {
						list.set(i, newVal);
						result = true;
					}
				}
			} else {
				for (int i=0; i<size; i++) {
					if (oldVal.equals(list.get(i))) {
						list.set(i, newVal);
						result = true;
					}
				}
			}
		} else {
			ListIterator<T> itr=list.listIterator();
			if (oldVal==null) {
				for (int i=0; i<size; i++) {
					if (itr.next()==null) {
						itr.set(newVal);
						result = true;
					}
				}
			} else {
				for (int i=0; i<size; i++) {
					if (oldVal.equals(itr.next())) {
						itr.set(newVal);
						result = true;
					}
				}
			}
		}
		return result;
	}

	/**
	 * Returns the starting position of the first occurrence of the specified
	 * target list within the specified source list, or -1 if there is no
	 * such occurrence.  More formally, returns the lowest index <tt>i</tt>
	 * such that {@code source.subList(i, i+target.size()).equals(target)},
	 * or -1 if there is no such index.  (Returns -1 if
	 * {@code target.size() > source.size()})
	 *
	 * <p>This implementation uses the "brute force" technique of scanning
	 * over the source list, looking for a match with the target at each
	 * location in turn.
	 *
	 * @param source the list in which to search for the first occurrence
	 *        of <tt>target</tt>.
	 * @param target the list to search for as a subList of <tt>source</tt>.
	 * @return the starting position of the first occurrence of the specified
	 *         target list within the specified source list, or -1 if there
	 *         is no such occurrence.
	 * @since  1.4
	 */
	public static int indexOfSubList(List<?> source, List<?> target) {
		int sourceSize = source.size();
		int targetSize = target.size();
		int maxCandidate = sourceSize - targetSize;

		if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
				(source instanceof RandomAccess&&target instanceof RandomAccess)) {
			nextCand:
			for (int candidate = 0; candidate <= maxCandidate; candidate++) {
				for (int i=0, j=candidate; i<targetSize; i++, j++)
					if (!eq(target.get(i), source.get(j)))
						continue nextCand;  // Element mismatch, try next cand
				return candidate;  // All elements of candidate matched target
			}
		} else {  // Iterator version of above algorithm
			ListIterator<?> si = source.listIterator();
			nextCand:
			for (int candidate = 0; candidate <= maxCandidate; candidate++) {
				ListIterator<?> ti = target.listIterator();
				for (int i=0; i<targetSize; i++) {
					if (!eq(ti.next(), si.next())) {
						// Back up source iterator to next candidate
						for (int j=0; j<i; j++)
							si.previous();
						continue nextCand;
					}
				}
				return candidate;
			}
		}
		return -1;  // No candidate matched the target
	}

	/**
	 * Returns the starting position of the last occurrence of the specified
	 * target list within the specified source list, or -1 if there is no such
	 * occurrence.  More formally, returns the highest index <tt>i</tt>
	 * such that {@code source.subList(i, i+target.size()).equals(target)},
	 * or -1 if there is no such index.  (Returns -1 if
	 * {@code target.size() > source.size()})
	 *
	 * <p>This implementation uses the "brute force" technique of iterating
	 * over the source list, looking for a match with the target at each
	 * location in turn.
	 *
	 * @param source the list in which to search for the last occurrence
	 *        of <tt>target</tt>.
	 * @param target the list to search for as a subList of <tt>source</tt>.
	 * @return the starting position of the last occurrence of the specified
	 *         target list within the specified source list, or -1 if there
	 *         is no such occurrence.
	 * @since  1.4
	 */
	public static int lastIndexOfSubList(List<?> source, List<?> target) {
		int sourceSize = source.size();
		int targetSize = target.size();
		int maxCandidate = sourceSize - targetSize;

		if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
				source instanceof RandomAccess) {   // Index access version
			nextCand:
			for (int candidate = maxCandidate; candidate >= 0; candidate--) {
				for (int i=0, j=candidate; i<targetSize; i++, j++)
					if (!eq(target.get(i), source.get(j)))
						continue nextCand;  // Element mismatch, try next cand
				return candidate;  // All elements of candidate matched target
			}
		} else {  // Iterator version of above algorithm
			if (maxCandidate < 0)
				return -1;
			ListIterator<?> si = source.listIterator(maxCandidate);
			nextCand:
			for (int candidate = maxCandidate; candidate >= 0; candidate--) {
				ListIterator<?> ti = target.listIterator();
				for (int i=0; i<targetSize; i++) {
					if (!eq(ti.next(), si.next())) {
						if (candidate != 0) {
							// Back up source iterator to next candidate
							for (int j=0; j<=i+1; j++)
								si.previous();
						}
						continue nextCand;
					}
				}
				return candidate;
			}
		}
		return -1;  // No candidate matched the target
	}


	// Unmodifiable Wrappers

	/**
	 * Returns an unmodifiable view of the specified collection.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * collections.  Query operations on the returned collection "read through"
	 * to the specified collection, and attempts to modify the returned
	 * collection, whether direct or via its iterator, result in an
	 * <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned collection does <i>not</i> pass the hashCode and equals
	 * operations through to the backing collection, but relies on
	 * <tt>Object</tt>'s <tt>equals</tt> and <tt>hashCode</tt> methods.  This
	 * is necessary to preserve the contracts of these operations in the case
	 * that the backing collection is a set or a list.<p>
	 *
	 * The returned collection will be serializable if the specified collection
	 * is serializable.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  c the collection for which an unmodifiable view is to be
	 *         returned.
	 * @return an unmodifiable view of the specified collection.
	 */
	public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
		return new UnmodifiableCollection<>(c);
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
		private static final long serialVersionUID = 1820017752578914078L;

		final Collection<? extends E> c;

		UnmodifiableCollection(Collection<? extends E> c) {
			if (c==null)
				throw new NullPointerException();
			this.c = c;
		}

		public int size()                   {return c.size();}
		public boolean isEmpty()            {return c.isEmpty();}
		public boolean contains(Object o)   {return c.contains(o);}
		public Object[] toArray()           {return c.toArray();}
		public <T> T[] toArray(T[] a)       {return c.toArray(a);}
		public String toString()            {return c.toString();}

		public Iterator<E> iterator() {
			return new Iterator<E>() {
				private final Iterator<? extends E> i = c.iterator();

				public boolean hasNext() {return i.hasNext();}
				public E next()          {return i.next();}
				public void remove() {
					throw new UnsupportedOperationException();
				}
				@Override
				public void forEachRemaining(Consumer<? super E> action) {
					// Use backing collection version
					i.forEachRemaining(action);
				}
			};
		}

		public boolean add(E e) {
			throw new UnsupportedOperationException();
		}
		public boolean remove(Object o) {
			throw new UnsupportedOperationException();
		}

		public boolean containsAll(Collection<?> coll) {
			return c.containsAll(coll);
		}
		public boolean addAll(Collection<? extends E> coll) {
			throw new UnsupportedOperationException();
		}
		public boolean removeAll(Collection<?> coll) {
			throw new UnsupportedOperationException();
		}
		public boolean retainAll(Collection<?> coll) {
			throw new UnsupportedOperationException();
		}
		public void clear() {
			throw new UnsupportedOperationException();
		}

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			c.forEach(action);
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			throw new UnsupportedOperationException();
		}
		@SuppressWarnings("unchecked")
		@Override
		public Spliterator<E> spliterator() {
			return (Spliterator<E>)c.spliterator();
		}
		@SuppressWarnings("unchecked")
		@Override
		public Stream<E> stream() {
			return (Stream<E>)c.stream();
		}
		@SuppressWarnings("unchecked")
		@Override
		public Stream<E> parallelStream() {
			return (Stream<E>)c.parallelStream();
		}
	}

	/**
	 * Returns an unmodifiable view of the specified set.  This method allows
	 * modules to provide users with "read-only" access to internal sets.
	 * Query operations on the returned set "read through" to the specified
	 * set, and attempts to modify the returned set, whether direct or via its
	 * iterator, result in an <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned set will be serializable if the specified set
	 * is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param  s the set for which an unmodifiable view is to be returned.
	 * @return an unmodifiable view of the specified set.
	 */
	public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
		return new UnmodifiableSet<>(s);
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
			implements Set<E>, Serializable {
		private static final long serialVersionUID = -9215047833775013803L;

		UnmodifiableSet(Set<? extends E> s)     {super(s);}
		public boolean equals(Object o) {return o == this || c.equals(o);}
		public int hashCode()           {return c.hashCode();}
	}

	/**
	 * Returns an unmodifiable view of the specified sorted set.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * sorted sets.  Query operations on the returned sorted set "read
	 * through" to the specified sorted set.  Attempts to modify the returned
	 * sorted set, whether direct, via its iterator, or via its
	 * <tt>subSet</tt>, <tt>headSet</tt>, or <tt>tailSet</tt> views, result in
	 * an <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned sorted set will be serializable if the specified sorted set
	 * is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param s the sorted set for which an unmodifiable view is to be
	 *        returned.
	 * @return an unmodifiable view of the specified sorted set.
	 */
	public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
		return new UnmodifiableSortedSet<>(s);
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableSortedSet<E>
			extends UnmodifiableSet<E>
			implements SortedSet<E>, Serializable {
		private static final long serialVersionUID = -4929149591599911165L;
		private final SortedSet<E> ss;

		UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}

		public Comparator<? super E> comparator() {return ss.comparator();}

		public SortedSet<E> subSet(E fromElement, E toElement) {
			return new UnmodifiableSortedSet<>(ss.subSet(fromElement,toElement));
		}
		public SortedSet<E> headSet(E toElement) {
			return new UnmodifiableSortedSet<>(ss.headSet(toElement));
		}
		public SortedSet<E> tailSet(E fromElement) {
			return new UnmodifiableSortedSet<>(ss.tailSet(fromElement));
		}

		public E first()                   {return ss.first();}
		public E last()                    {return ss.last();}
	}

	/**
	 * Returns an unmodifiable view of the specified navigable set.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * navigable sets.  Query operations on the returned navigable set "read
	 * through" to the specified navigable set.  Attempts to modify the returned
	 * navigable set, whether direct, via its iterator, or via its
	 * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in
	 * an {@code UnsupportedOperationException}.<p>
	 *
	 * The returned navigable set will be serializable if the specified
	 * navigable set is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param s the navigable set for which an unmodifiable view is to be
	 *        returned
	 * @return an unmodifiable view of the specified navigable set
	 * @since 1.8
	 */
	public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) {
		return new UnmodifiableNavigableSet<>(s);
	}

	/**
	 * Wraps a navigable set and disables all of the mutative operations.
	 *
	 * @param <E> type of elements
	 * @serial include
	 */
	static class UnmodifiableNavigableSet<E>
			extends UnmodifiableSortedSet<E>
			implements NavigableSet<E>, Serializable {

		private static final long serialVersionUID = -6027448201786391929L;

		/**
		 * A singleton empty unmodifiable navigable set used for
		 * {@link #emptyNavigableSet()}.
		 *
		 * @param <E> type of elements, if there were any, and bounds
		 */
		private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E>
				implements Serializable {
			private static final long serialVersionUID = -6291252904449939134L;

			public EmptyNavigableSet() {
				super(new TreeSet<E>());
			}

			private Object readResolve()        { return EMPTY_NAVIGABLE_SET; }
		}

		@SuppressWarnings("rawtypes")
		private static final NavigableSet<?> EMPTY_NAVIGABLE_SET =
				new EmptyNavigableSet<>();

		/**
		 * The instance we are protecting.
		 */
		private final NavigableSet<E> ns;

		UnmodifiableNavigableSet(NavigableSet<E> s)         {super(s); ns = s;}

		public E lower(E e)                             { return ns.lower(e); }
		public E floor(E e)                             { return ns.floor(e); }
		public E ceiling(E e)                         { return ns.ceiling(e); }
		public E higher(E e)                           { return ns.higher(e); }
		public E pollFirst()     { throw new UnsupportedOperationException(); }
		public E pollLast()      { throw new UnsupportedOperationException(); }
		public NavigableSet<E> descendingSet()
		{ return new UnmodifiableNavigableSet<>(ns.descendingSet()); }
		public Iterator<E> descendingIterator()
		{ return descendingSet().iterator(); }

		public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
			return new UnmodifiableNavigableSet<>(
					ns.subSet(fromElement, fromInclusive, toElement, toInclusive));
		}

		public NavigableSet<E> headSet(E toElement, boolean inclusive) {
			return new UnmodifiableNavigableSet<>(
					ns.headSet(toElement, inclusive));
		}

		public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
			return new UnmodifiableNavigableSet<>(
					ns.tailSet(fromElement, inclusive));
		}
	}

	/**
	 * Returns an unmodifiable view of the specified list.  This method allows
	 * modules to provide users with "read-only" access to internal
	 * lists.  Query operations on the returned list "read through" to the
	 * specified list, and attempts to modify the returned list, whether
	 * direct or via its iterator, result in an
	 * <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned list will be serializable if the specified list
	 * is serializable. Similarly, the returned list will implement
	 * {@link RandomAccess} if the specified list does.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list for which an unmodifiable view is to be returned.
	 * @return an unmodifiable view of the specified list.
	 */
	public static <T> List<T> unmodifiableList(List<? extends T> list) {
		return (list instanceof RandomAccess ?
				new UnmodifiableRandomAccessList<>(list) :
				new UnmodifiableList<>(list));
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableList<E> extends UnmodifiableCollection<E>
			implements List<E> {
		private static final long serialVersionUID = -283967356065247728L;

		final List<? extends E> list;

		UnmodifiableList(List<? extends E> list) {
			super(list);
			this.list = list;
		}

		public boolean equals(Object o) {return o == this || list.equals(o);}
		public int hashCode()           {return list.hashCode();}

		public E get(int index) {return list.get(index);}
		public E set(int index, E element) {
			throw new UnsupportedOperationException();
		}
		public void add(int index, E element) {
			throw new UnsupportedOperationException();
		}
		public E remove(int index) {
			throw new UnsupportedOperationException();
		}
		public int indexOf(Object o)            {return list.indexOf(o);}
		public int lastIndexOf(Object o)        {return list.lastIndexOf(o);}
		public boolean addAll(int index, Collection<? extends E> c) {
			throw new UnsupportedOperationException();
		}

		@Override
		public void replaceAll(UnaryOperator<E> operator) {
			throw new UnsupportedOperationException();
		}
		@Override
		public void sort(Comparator<? super E> c) {
			throw new UnsupportedOperationException();
		}

		public ListIterator<E> listIterator()   {return listIterator(0);}

		public ListIterator<E> listIterator(final int index) {
			return new ListIterator<E>() {
				private final ListIterator<? extends E> i
						= list.listIterator(index);

				public boolean hasNext()     {return i.hasNext();}
				public E next()              {return i.next();}
				public boolean hasPrevious() {return i.hasPrevious();}
				public E previous()          {return i.previous();}
				public int nextIndex()       {return i.nextIndex();}
				public int previousIndex()   {return i.previousIndex();}

				public void remove() {
					throw new UnsupportedOperationException();
				}
				public void set(E e) {
					throw new UnsupportedOperationException();
				}
				public void add(E e) {
					throw new UnsupportedOperationException();
				}

				@Override
				public void forEachRemaining(Consumer<? super E> action) {
					i.forEachRemaining(action);
				}
			};
		}

		public List<E> subList(int fromIndex, int toIndex) {
			return new UnmodifiableList<>(list.subList(fromIndex, toIndex));
		}

		/**
		 * UnmodifiableRandomAccessList instances are serialized as
		 * UnmodifiableList instances to allow them to be deserialized
		 * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
		 * This method inverts the transformation.  As a beneficial
		 * side-effect, it also grafts the RandomAccess marker onto
		 * UnmodifiableList instances that were serialized in pre-1.4 JREs.
		 *
		 * Note: Unfortunately, UnmodifiableRandomAccessList instances
		 * serialized in 1.4.1 and deserialized in 1.4 will become
		 * UnmodifiableList instances, as this method was missing in 1.4.
		 */
		private Object readResolve() {
			return (list instanceof RandomAccess
					? new UnmodifiableRandomAccessList<>(list)
					: this);
		}
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
			implements RandomAccess
	{
		UnmodifiableRandomAccessList(List<? extends E> list) {
			super(list);
		}

		public List<E> subList(int fromIndex, int toIndex) {
			return new UnmodifiableRandomAccessList<>(
					list.subList(fromIndex, toIndex));
		}

		private static final long serialVersionUID = -2542308836966382001L;

		/**
		 * Allows instances to be deserialized in pre-1.4 JREs (which do
		 * not have UnmodifiableRandomAccessList).  UnmodifiableList has
		 * a readResolve method that inverts this transformation upon
		 * deserialization.
		 */
		private Object writeReplace() {
			return new UnmodifiableList<>(list);
		}
	}

	/**
	 * Returns an unmodifiable view of the specified map.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * maps.  Query operations on the returned map "read through"
	 * to the specified map, and attempts to modify the returned
	 * map, whether direct or via its collection views, result in an
	 * <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned map will be serializable if the specified map
	 * is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param  m the map for which an unmodifiable view is to be returned.
	 * @return an unmodifiable view of the specified map.
	 */
	public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
		return new UnmodifiableMap<>(m);
	}

	/**
	 * @serial include
	 */
	private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
		private static final long serialVersionUID = -1034234728574286014L;

		private final Map<? extends K, ? extends V> m;

		UnmodifiableMap(Map<? extends K, ? extends V> m) {
			if (m==null)
				throw new NullPointerException();
			this.m = m;
		}

		public int size()                        {return m.size();}
		public boolean isEmpty()                 {return m.isEmpty();}
		public boolean containsKey(Object key)   {return m.containsKey(key);}
		public boolean containsValue(Object val) {return m.containsValue(val);}
		public V get(Object key)                 {return m.get(key);}

		public V put(K key, V value) {
			throw new UnsupportedOperationException();
		}
		public V remove(Object key) {
			throw new UnsupportedOperationException();
		}
		public void putAll(Map<? extends K, ? extends V> m) {
			throw new UnsupportedOperationException();
		}
		public void clear() {
			throw new UnsupportedOperationException();
		}

		private transient Set<K> keySet;
		private transient Set<Map.Entry<K,V>> entrySet;
		private transient Collection<V> values;

		public Set<K> keySet() {
			if (keySet==null)
				keySet = unmodifiableSet(m.keySet());
			return keySet;
		}

		public Set<Map.Entry<K,V>> entrySet() {
			if (entrySet==null)
				entrySet = new UnmodifiableEntrySet<>(m.entrySet());
			return entrySet;
		}

		public Collection<V> values() {
			if (values==null)
				values = unmodifiableCollection(m.values());
			return values;
		}

		public boolean equals(Object o) {return o == this || m.equals(o);}
		public int hashCode()           {return m.hashCode();}
		public String toString()        {return m.toString();}

		// Override default methods in Map
		@Override
		@SuppressWarnings("unchecked")
		public V getOrDefault(Object k, V defaultValue) {
			// Safe cast as we don't change the value
			return ((Map<K, V>)m).getOrDefault(k, defaultValue);
		}

		@Override
		public void forEach(BiConsumer<? super K, ? super V> action) {
			m.forEach(action);
		}

		@Override
		public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V putIfAbsent(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean remove(Object key, Object value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean replace(K key, V oldValue, V newValue) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V replace(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfPresent(K key,
		                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V compute(K key,
		                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V merge(K key, V value,
		               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		/**
		 * We need this class in addition to UnmodifiableSet as
		 * Map.Entries themselves permit modification of the backing Map
		 * via their setValue operation.  This class is subtle: there are
		 * many possible attacks that must be thwarted.
		 *
		 * @serial include
		 */
		static class UnmodifiableEntrySet<K,V>
				extends UnmodifiableSet<Map.Entry<K,V>> {
			private static final long serialVersionUID = 7854390611657943733L;

			@SuppressWarnings({"unchecked", "rawtypes"})
			UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
				// Need to cast to raw in order to work around a limitation in the type system
				super((Set)s);
			}

			static <K, V> Consumer<Map.Entry<K, V>> entryConsumer(Consumer<? super Entry<K, V>> action) {
				return e -> action.accept(new UnmodifiableEntry<>(e));
			}

			public void forEach(Consumer<? super Entry<K, V>> action) {
				Objects.requireNonNull(action);
				c.forEach(entryConsumer(action));
			}

			static final class UnmodifiableEntrySetSpliterator<K, V>
					implements Spliterator<Entry<K,V>> {
				final Spliterator<Map.Entry<K, V>> s;

				UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) {
					this.s = s;
				}

				@Override
				public boolean tryAdvance(Consumer<? super Entry<K, V>> action) {
					Objects.requireNonNull(action);
					return s.tryAdvance(entryConsumer(action));
				}

				@Override
				public void forEachRemaining(Consumer<? super Entry<K, V>> action) {
					Objects.requireNonNull(action);
					s.forEachRemaining(entryConsumer(action));
				}

				@Override
				public Spliterator<Entry<K, V>> trySplit() {
					Spliterator<Entry<K, V>> split = s.trySplit();
					return split == null
							? null
							: new UnmodifiableEntrySetSpliterator<>(split);
				}

				@Override
				public long estimateSize() {
					return s.estimateSize();
				}

				@Override
				public long getExactSizeIfKnown() {
					return s.getExactSizeIfKnown();
				}

				@Override
				public int characteristics() {
					return s.characteristics();
				}

				@Override
				public boolean hasCharacteristics(int characteristics) {
					return s.hasCharacteristics(characteristics);
				}

				@Override
				public Comparator<? super Entry<K, V>> getComparator() {
					return s.getComparator();
				}
			}

			@SuppressWarnings("unchecked")
			public Spliterator<Entry<K,V>> spliterator() {
				return new UnmodifiableEntrySetSpliterator<>(
						(Spliterator<Map.Entry<K, V>>) c.spliterator());
			}

			@Override
			public Stream<Entry<K,V>> stream() {
				return StreamSupport.stream(spliterator(), false);
			}

			@Override
			public Stream<Entry<K,V>> parallelStream() {
				return StreamSupport.stream(spliterator(), true);
			}

			public Iterator<Map.Entry<K,V>> iterator() {
				return new Iterator<Map.Entry<K,V>>() {
					private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();

					public boolean hasNext() {
						return i.hasNext();
					}
					public Map.Entry<K,V> next() {
						return new UnmodifiableEntry<>(i.next());
					}
					public void remove() {
						throw new UnsupportedOperationException();
					}
				};
			}

			@SuppressWarnings("unchecked")
			public Object[] toArray() {
				Object[] a = c.toArray();
				for (int i=0; i<a.length; i++)
					a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)a[i]);
				return a;
			}

			@SuppressWarnings("unchecked")
			public <T> T[] toArray(T[] a) {
				// We don't pass a to c.toArray, to avoid window of
				// vulnerability wherein an unscrupulous multithreaded client
				// could get his hands on raw (unwrapped) Entries from c.
				Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));

				for (int i=0; i<arr.length; i++)
					arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>)arr[i]);

				if (arr.length > a.length)
					return (T[])arr;

				System.arraycopy(arr, 0, a, 0, arr.length);
				if (a.length > arr.length)
					a[arr.length] = null;
				return a;
			}

			/**
			 * This method is overridden to protect the backing set against
			 * an object with a nefarious equals function that senses
			 * that the equality-candidate is Map.Entry and calls its
			 * setValue method.
			 */
			public boolean contains(Object o) {
				if (!(o instanceof Map.Entry))
					return false;
				return c.contains(
						new UnmodifiableEntry<>((Map.Entry<?,?>) o));
			}

			/**
			 * The next two methods are overridden to protect against
			 * an unscrupulous List whose contains(Object o) method senses
			 * when o is a Map.Entry, and calls o.setValue.
			 */
			public boolean containsAll(Collection<?> coll) {
				for (Object e : coll) {
					if (!contains(e)) // Invokes safe contains() above
						return false;
				}
				return true;
			}
			public boolean equals(Object o) {
				if (o == this)
					return true;

				if (!(o instanceof Set))
					return false;
				Set<?> s = (Set<?>) o;
				if (s.size() != c.size())
					return false;
				return containsAll(s); // Invokes safe containsAll() above
			}

			/**
			 * This "wrapper class" serves two purposes: it prevents
			 * the client from modifying the backing Map, by short-circuiting
			 * the setValue method, and it protects the backing Map against
			 * an ill-behaved Map.Entry that attempts to modify another
			 * Map Entry when asked to perform an equality check.
			 */
			private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
				private Map.Entry<? extends K, ? extends V> e;

				UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e)
				{this.e = Objects.requireNonNull(e);}

				public K getKey()        {return e.getKey();}
				public V getValue()      {return e.getValue();}
				public V setValue(V value) {
					throw new UnsupportedOperationException();
				}
				public int hashCode()    {return e.hashCode();}
				public boolean equals(Object o) {
					if (this == o)
						return true;
					if (!(o instanceof Map.Entry))
						return false;
					Map.Entry<?,?> t = (Map.Entry<?,?>)o;
					return eq(e.getKey(),   t.getKey()) &&
							eq(e.getValue(), t.getValue());
				}
				public String toString() {return e.toString();}
			}
		}
	}

	/**
	 * Returns an unmodifiable view of the specified sorted map.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * sorted maps.  Query operations on the returned sorted map "read through"
	 * to the specified sorted map.  Attempts to modify the returned
	 * sorted map, whether direct, via its collection views, or via its
	 * <tt>subMap</tt>, <tt>headMap</tt>, or <tt>tailMap</tt> views, result in
	 * an <tt>UnsupportedOperationException</tt>.<p>
	 *
	 * The returned sorted map will be serializable if the specified sorted map
	 * is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param m the sorted map for which an unmodifiable view is to be
	 *        returned.
	 * @return an unmodifiable view of the specified sorted map.
	 */
	public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
		return new UnmodifiableSortedMap<>(m);
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableSortedMap<K,V>
			extends UnmodifiableMap<K,V>
			implements SortedMap<K,V>, Serializable {
		private static final long serialVersionUID = -8806743815996713206L;

		private final SortedMap<K, ? extends V> sm;

		UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m; }
		public Comparator<? super K> comparator()   { return sm.comparator(); }
		public SortedMap<K,V> subMap(K fromKey, K toKey)
		{ return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); }
		public SortedMap<K,V> headMap(K toKey)
		{ return new UnmodifiableSortedMap<>(sm.headMap(toKey)); }
		public SortedMap<K,V> tailMap(K fromKey)
		{ return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); }
		public K firstKey()                           { return sm.firstKey(); }
		public K lastKey()                             { return sm.lastKey(); }
	}

	/**
	 * Returns an unmodifiable view of the specified navigable map.  This method
	 * allows modules to provide users with "read-only" access to internal
	 * navigable maps.  Query operations on the returned navigable map "read
	 * through" to the specified navigable map.  Attempts to modify the returned
	 * navigable map, whether direct, via its collection views, or via its
	 * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in
	 * an {@code UnsupportedOperationException}.<p>
	 *
	 * The returned navigable map will be serializable if the specified
	 * navigable map is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param m the navigable map for which an unmodifiable view is to be
	 *        returned
	 * @return an unmodifiable view of the specified navigable map
	 * @since 1.8
	 */
	public static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) {
		return new UnmodifiableNavigableMap<>(m);
	}

	/**
	 * @serial include
	 */
	static class UnmodifiableNavigableMap<K,V>
			extends UnmodifiableSortedMap<K,V>
			implements NavigableMap<K,V>, Serializable {
		private static final long serialVersionUID = -4858195264774772197L;

		/**
		 * A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve
		 * to preserve singleton property.
		 *
		 * @param <K> type of keys, if there were any, and of bounds
		 * @param <V> type of values, if there were any
		 */
		private static class EmptyNavigableMap<K,V> extends UnmodifiableNavigableMap<K,V>
				implements Serializable {

			private static final long serialVersionUID = -2239321462712562324L;

			EmptyNavigableMap()                       { super(new TreeMap<K,V>()); }

			@Override
			public NavigableSet<K> navigableKeySet()
			{ return emptyNavigableSet(); }

			private Object readResolve()        { return EMPTY_NAVIGABLE_MAP; }
		}

		/**
		 * Singleton for {@link emptyNavigableMap()} which is also immutable.
		 */
		private static final EmptyNavigableMap<?,?> EMPTY_NAVIGABLE_MAP =
				new EmptyNavigableMap<>();

		/**
		 * The instance we wrap and protect.
		 */
		private final NavigableMap<K, ? extends V> nm;

		UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m)
		{super(m); nm = m;}

		public K lowerKey(K key)                   { return nm.lowerKey(key); }
		public K floorKey(K key)                   { return nm.floorKey(key); }
		public K ceilingKey(K key)               { return nm.ceilingKey(key); }
		public K higherKey(K key)                 { return nm.higherKey(key); }

		@SuppressWarnings("unchecked")
		public Entry<K, V> lowerEntry(K key) {
			Entry<K,V> lower = (Entry<K, V>) nm.lowerEntry(key);
			return (null != lower)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower)
					: null;
		}

		@SuppressWarnings("unchecked")
		public Entry<K, V> floorEntry(K key) {
			Entry<K,V> floor = (Entry<K, V>) nm.floorEntry(key);
			return (null != floor)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor)
					: null;
		}

		@SuppressWarnings("unchecked")
		public Entry<K, V> ceilingEntry(K key) {
			Entry<K,V> ceiling = (Entry<K, V>) nm.ceilingEntry(key);
			return (null != ceiling)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling)
					: null;
		}


		@SuppressWarnings("unchecked")
		public Entry<K, V> higherEntry(K key) {
			Entry<K,V> higher = (Entry<K, V>) nm.higherEntry(key);
			return (null != higher)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher)
					: null;
		}

		@SuppressWarnings("unchecked")
		public Entry<K, V> firstEntry() {
			Entry<K,V> first = (Entry<K, V>) nm.firstEntry();
			return (null != first)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(first)
					: null;
		}

		@SuppressWarnings("unchecked")
		public Entry<K, V> lastEntry() {
			Entry<K,V> last = (Entry<K, V>) nm.lastEntry();
			return (null != last)
					? new UnmodifiableEntrySet.UnmodifiableEntry<>(last)
					: null;
		}

		public Entry<K, V> pollFirstEntry()
		{ throw new UnsupportedOperationException(); }
		public Entry<K, V> pollLastEntry()
		{ throw new UnsupportedOperationException(); }
		public NavigableMap<K, V> descendingMap()
		{ return unmodifiableNavigableMap(nm.descendingMap()); }
		public NavigableSet<K> navigableKeySet()
		{ return unmodifiableNavigableSet(nm.navigableKeySet()); }
		public NavigableSet<K> descendingKeySet()
		{ return unmodifiableNavigableSet(nm.descendingKeySet()); }

		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return unmodifiableNavigableMap(
					nm.subMap(fromKey, fromInclusive, toKey, toInclusive));
		}

		public NavigableMap<K, V> headMap(K toKey, boolean inclusive)
		{ return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); }
		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive)
		{ return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); }
	}

	// Synch Wrappers

	/**
	 * Returns a synchronized (thread-safe) collection backed by the specified
	 * collection.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing collection is accomplished
	 * through the returned collection.<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * collection when traversing it via {@link Iterator}, {@link Spliterator}
	 * or {@link Stream}:
	 * <pre>
	 *  Collection c = Collections.synchronizedCollection(myCollection);
	 *     ...
	 *  synchronized (c) {
	 *      Iterator i = c.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *         foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned collection does <i>not</i> pass the {@code hashCode}
	 * and {@code equals} operations through to the backing collection, but
	 * relies on {@code Object}'s equals and hashCode methods.  This is
	 * necessary to preserve the contracts of these operations in the case
	 * that the backing collection is a set or a list.<p>
	 *
	 * The returned collection will be serializable if the specified collection
	 * is serializable.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param  c the collection to be "wrapped" in a synchronized collection.
	 * @return a synchronized view of the specified collection.
	 */
	public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
		return new SynchronizedCollection<>(c);
	}

	static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
		return new SynchronizedCollection<>(c, mutex);
	}

	/**
	 * @serial include
	 */
	static class SynchronizedCollection<E> implements Collection<E>, Serializable {
		private static final long serialVersionUID = 3053995032091335093L;

		final Collection<E> c;  // Backing Collection
		final Object mutex;     // Object on which to synchronize

		SynchronizedCollection(Collection<E> c) {
			this.c = Objects.requireNonNull(c);
			mutex = this;
		}

		SynchronizedCollection(Collection<E> c, Object mutex) {
			this.c = Objects.requireNonNull(c);
			this.mutex = Objects.requireNonNull(mutex);
		}

		public int size() {
			synchronized (mutex) {return c.size();}
		}
		public boolean isEmpty() {
			synchronized (mutex) {return c.isEmpty();}
		}
		public boolean contains(Object o) {
			synchronized (mutex) {return c.contains(o);}
		}
		public Object[] toArray() {
			synchronized (mutex) {return c.toArray();}
		}
		public <T> T[] toArray(T[] a) {
			synchronized (mutex) {return c.toArray(a);}
		}

		public Iterator<E> iterator() {
			return c.iterator(); // Must be manually synched by user!
		}

		public boolean add(E e) {
			synchronized (mutex) {return c.add(e);}
		}
		public boolean remove(Object o) {
			synchronized (mutex) {return c.remove(o);}
		}

		public boolean containsAll(Collection<?> coll) {
			synchronized (mutex) {return c.containsAll(coll);}
		}
		public boolean addAll(Collection<? extends E> coll) {
			synchronized (mutex) {return c.addAll(coll);}
		}
		public boolean removeAll(Collection<?> coll) {
			synchronized (mutex) {return c.removeAll(coll);}
		}
		public boolean retainAll(Collection<?> coll) {
			synchronized (mutex) {return c.retainAll(coll);}
		}
		public void clear() {
			synchronized (mutex) {c.clear();}
		}
		public String toString() {
			synchronized (mutex) {return c.toString();}
		}
		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> consumer) {
			synchronized (mutex) {c.forEach(consumer);}
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			synchronized (mutex) {return c.removeIf(filter);}
		}
		@Override
		public Spliterator<E> spliterator() {
			return c.spliterator(); // Must be manually synched by user!
		}
		@Override
		public Stream<E> stream() {
			return c.stream(); // Must be manually synched by user!
		}
		@Override
		public Stream<E> parallelStream() {
			return c.parallelStream(); // Must be manually synched by user!
		}
		private void writeObject(ObjectOutputStream s) throws IOException {
			synchronized (mutex) {s.defaultWriteObject();}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) set backed by the specified
	 * set.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing set is accomplished
	 * through the returned set.<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * set when iterating over it:
	 * <pre>
	 *  Set s = Collections.synchronizedSet(new HashSet());
	 *      ...
	 *  synchronized (s) {
	 *      Iterator i = s.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned set will be serializable if the specified set is
	 * serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param  s the set to be "wrapped" in a synchronized set.
	 * @return a synchronized view of the specified set.
	 */
	public static <T> Set<T> synchronizedSet(Set<T> s) {
		return new SynchronizedSet<>(s);
	}

	static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
		return new SynchronizedSet<>(s, mutex);
	}

	/**
	 * @serial include
	 */
	static class SynchronizedSet<E>
			extends SynchronizedCollection<E>
			implements Set<E> {
		private static final long serialVersionUID = 487447009682186044L;

		SynchronizedSet(Set<E> s) {
			super(s);
		}
		SynchronizedSet(Set<E> s, Object mutex) {
			super(s, mutex);
		}

		public boolean equals(Object o) {
			if (this == o)
				return true;
			synchronized (mutex) {return c.equals(o);}
		}
		public int hashCode() {
			synchronized (mutex) {return c.hashCode();}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) sorted set backed by the specified
	 * sorted set.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing sorted set is accomplished
	 * through the returned sorted set (or its views).<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * sorted set when iterating over it or any of its <tt>subSet</tt>,
	 * <tt>headSet</tt>, or <tt>tailSet</tt> views.
	 * <pre>
	 *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
	 *      ...
	 *  synchronized (s) {
	 *      Iterator i = s.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * or:
	 * <pre>
	 *  SortedSet s = Collections.synchronizedSortedSet(new TreeSet());
	 *  SortedSet s2 = s.headSet(foo);
	 *      ...
	 *  synchronized (s) {  // Note: s, not s2!!!
	 *      Iterator i = s2.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned sorted set will be serializable if the specified
	 * sorted set is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param  s the sorted set to be "wrapped" in a synchronized sorted set.
	 * @return a synchronized view of the specified sorted set.
	 */
	public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
		return new SynchronizedSortedSet<>(s);
	}

	/**
	 * @serial include
	 */
	static class SynchronizedSortedSet<E>
			extends SynchronizedSet<E>
			implements SortedSet<E>
	{
		private static final long serialVersionUID = 8695801310862127406L;

		private final SortedSet<E> ss;

		SynchronizedSortedSet(SortedSet<E> s) {
			super(s);
			ss = s;
		}
		SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
			super(s, mutex);
			ss = s;
		}

		public Comparator<? super E> comparator() {
			synchronized (mutex) {return ss.comparator();}
		}

		public SortedSet<E> subSet(E fromElement, E toElement) {
			synchronized (mutex) {
				return new SynchronizedSortedSet<>(
						ss.subSet(fromElement, toElement), mutex);
			}
		}
		public SortedSet<E> headSet(E toElement) {
			synchronized (mutex) {
				return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex);
			}
		}
		public SortedSet<E> tailSet(E fromElement) {
			synchronized (mutex) {
				return new SynchronizedSortedSet<>(ss.tailSet(fromElement),mutex);
			}
		}

		public E first() {
			synchronized (mutex) {return ss.first();}
		}
		public E last() {
			synchronized (mutex) {return ss.last();}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) navigable set backed by the
	 * specified navigable set.  In order to guarantee serial access, it is
	 * critical that <strong>all</strong> access to the backing navigable set is
	 * accomplished through the returned navigable set (or its views).<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * navigable set when iterating over it or any of its {@code subSet},
	 * {@code headSet}, or {@code tailSet} views.
	 * <pre>
	 *  NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
	 *      ...
	 *  synchronized (s) {
	 *      Iterator i = s.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * or:
	 * <pre>
	 *  NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet());
	 *  NavigableSet s2 = s.headSet(foo, true);
	 *      ...
	 *  synchronized (s) {  // Note: s, not s2!!!
	 *      Iterator i = s2.iterator(); // Must be in the synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned navigable set will be serializable if the specified
	 * navigable set is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param  s the navigable set to be "wrapped" in a synchronized navigable
	 * set
	 * @return a synchronized view of the specified navigable set
	 * @since 1.8
	 */
	public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) {
		return new SynchronizedNavigableSet<>(s);
	}

	/**
	 * @serial include
	 */
	static class SynchronizedNavigableSet<E>
			extends SynchronizedSortedSet<E>
			implements NavigableSet<E>
	{
		private static final long serialVersionUID = -5505529816273629798L;

		private final NavigableSet<E> ns;

		SynchronizedNavigableSet(NavigableSet<E> s) {
			super(s);
			ns = s;
		}

		SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) {
			super(s, mutex);
			ns = s;
		}
		public E lower(E e)      { synchronized (mutex) {return ns.lower(e);} }
		public E floor(E e)      { synchronized (mutex) {return ns.floor(e);} }
		public E ceiling(E e)  { synchronized (mutex) {return ns.ceiling(e);} }
		public E higher(E e)    { synchronized (mutex) {return ns.higher(e);} }
		public E pollFirst()  { synchronized (mutex) {return ns.pollFirst();} }
		public E pollLast()    { synchronized (mutex) {return ns.pollLast();} }

		public NavigableSet<E> descendingSet() {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex);
			}
		}

		public Iterator<E> descendingIterator()
		{ synchronized (mutex) { return descendingSet().iterator(); } }

		public NavigableSet<E> subSet(E fromElement, E toElement) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex);
			}
		}
		public NavigableSet<E> headSet(E toElement) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex);
			}
		}
		public NavigableSet<E> tailSet(E fromElement) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex);
			}
		}

		public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex);
			}
		}

		public NavigableSet<E> headSet(E toElement, boolean inclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex);
			}
		}

		public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive), mutex);
			}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) list backed by the specified
	 * list.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing list is accomplished
	 * through the returned list.<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * list when iterating over it:
	 * <pre>
	 *  List list = Collections.synchronizedList(new ArrayList());
	 *      ...
	 *  synchronized (list) {
	 *      Iterator i = list.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned list will be serializable if the specified list is
	 * serializable.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param  list the list to be "wrapped" in a synchronized list.
	 * @return a synchronized view of the specified list.
	 */
	public static <T> List<T> synchronizedList(List<T> list) {
		return (list instanceof RandomAccess ?
				new SynchronizedRandomAccessList<>(list) :
				new SynchronizedList<>(list));
	}

	static <T> List<T> synchronizedList(List<T> list, Object mutex) {
		return (list instanceof RandomAccess ?
				new SynchronizedRandomAccessList<>(list, mutex) :
				new SynchronizedList<>(list, mutex));
	}

	/**
	 * @serial include
	 */
	static class SynchronizedList<E>
			extends SynchronizedCollection<E>
			implements List<E> {
		private static final long serialVersionUID = -7754090372962971524L;

		final List<E> list;

		SynchronizedList(List<E> list) {
			super(list);
			this.list = list;
		}
		SynchronizedList(List<E> list, Object mutex) {
			super(list, mutex);
			this.list = list;
		}

		public boolean equals(Object o) {
			if (this == o)
				return true;
			synchronized (mutex) {return list.equals(o);}
		}
		public int hashCode() {
			synchronized (mutex) {return list.hashCode();}
		}

		public E get(int index) {
			synchronized (mutex) {return list.get(index);}
		}
		public E set(int index, E element) {
			synchronized (mutex) {return list.set(index, element);}
		}
		public void add(int index, E element) {
			synchronized (mutex) {list.add(index, element);}
		}
		public E remove(int index) {
			synchronized (mutex) {return list.remove(index);}
		}

		public int indexOf(Object o) {
			synchronized (mutex) {return list.indexOf(o);}
		}
		public int lastIndexOf(Object o) {
			synchronized (mutex) {return list.lastIndexOf(o);}
		}

		public boolean addAll(int index, Collection<? extends E> c) {
			synchronized (mutex) {return list.addAll(index, c);}
		}

		public ListIterator<E> listIterator() {
			return list.listIterator(); // Must be manually synched by user
		}

		public ListIterator<E> listIterator(int index) {
			return list.listIterator(index); // Must be manually synched by user
		}

		public List<E> subList(int fromIndex, int toIndex) {
			synchronized (mutex) {
				return new SynchronizedList<>(list.subList(fromIndex, toIndex),
						mutex);
			}
		}

		@Override
		public void replaceAll(UnaryOperator<E> operator) {
			synchronized (mutex) {list.replaceAll(operator);}
		}
		@Override
		public void sort(Comparator<? super E> c) {
			synchronized (mutex) {list.sort(c);}
		}

		/**
		 * SynchronizedRandomAccessList instances are serialized as
		 * SynchronizedList instances to allow them to be deserialized
		 * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).
		 * This method inverts the transformation.  As a beneficial
		 * side-effect, it also grafts the RandomAccess marker onto
		 * SynchronizedList instances that were serialized in pre-1.4 JREs.
		 *
		 * Note: Unfortunately, SynchronizedRandomAccessList instances
		 * serialized in 1.4.1 and deserialized in 1.4 will become
		 * SynchronizedList instances, as this method was missing in 1.4.
		 */
		private Object readResolve() {
			return (list instanceof RandomAccess
					? new SynchronizedRandomAccessList<>(list)
					: this);
		}
	}

	/**
	 * @serial include
	 */
	static class SynchronizedRandomAccessList<E>
			extends SynchronizedList<E>
			implements RandomAccess {

		SynchronizedRandomAccessList(List<E> list) {
			super(list);
		}

		SynchronizedRandomAccessList(List<E> list, Object mutex) {
			super(list, mutex);
		}

		public List<E> subList(int fromIndex, int toIndex) {
			synchronized (mutex) {
				return new SynchronizedRandomAccessList<>(
						list.subList(fromIndex, toIndex), mutex);
			}
		}

		private static final long serialVersionUID = 1530674583602358482L;

		/**
		 * Allows instances to be deserialized in pre-1.4 JREs (which do
		 * not have SynchronizedRandomAccessList).  SynchronizedList has
		 * a readResolve method that inverts this transformation upon
		 * deserialization.
		 */
		private Object writeReplace() {
			return new SynchronizedList<>(list);
		}
	}

	/**
	 * Returns a synchronized (thread-safe) map backed by the specified
	 * map.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing map is accomplished
	 * through the returned map.<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * map when iterating over any of its collection views:
	 * <pre>
	 *  Map m = Collections.synchronizedMap(new HashMap());
	 *      ...
	 *  Set s = m.keySet();  // Needn't be in synchronized block
	 *      ...
	 *  synchronized (m) {  // Synchronizing on m, not s!
	 *      Iterator i = s.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned map will be serializable if the specified map is
	 * serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param  m the map to be "wrapped" in a synchronized map.
	 * @return a synchronized view of the specified map.
	 */
	public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
		return new SynchronizedMap<>(m);
	}

	/**
	 * @serial include
	 */
	private static class SynchronizedMap<K,V>
			implements Map<K,V>, Serializable {
		private static final long serialVersionUID = 1978198479659022715L;

		private final Map<K,V> m;     // Backing Map
		final Object      mutex;        // Object on which to synchronize

		SynchronizedMap(Map<K,V> m) {
			this.m = Objects.requireNonNull(m);
			mutex = this;
		}

		SynchronizedMap(Map<K,V> m, Object mutex) {
			this.m = m;
			this.mutex = mutex;
		}

		public int size() {
			synchronized (mutex) {return m.size();}
		}
		public boolean isEmpty() {
			synchronized (mutex) {return m.isEmpty();}
		}
		public boolean containsKey(Object key) {
			synchronized (mutex) {return m.containsKey(key);}
		}
		public boolean containsValue(Object value) {
			synchronized (mutex) {return m.containsValue(value);}
		}
		public V get(Object key) {
			synchronized (mutex) {return m.get(key);}
		}

		public V put(K key, V value) {
			synchronized (mutex) {return m.put(key, value);}
		}
		public V remove(Object key) {
			synchronized (mutex) {return m.remove(key);}
		}
		public void putAll(Map<? extends K, ? extends V> map) {
			synchronized (mutex) {m.putAll(map);}
		}
		public void clear() {
			synchronized (mutex) {m.clear();}
		}

		private transient Set<K> keySet;
		private transient Set<Map.Entry<K,V>> entrySet;
		private transient Collection<V> values;

		public Set<K> keySet() {
			synchronized (mutex) {
				if (keySet==null)
					keySet = new SynchronizedSet<>(m.keySet(), mutex);
				return keySet;
			}
		}

		public Set<Map.Entry<K,V>> entrySet() {
			synchronized (mutex) {
				if (entrySet==null)
					entrySet = new SynchronizedSet<>(m.entrySet(), mutex);
				return entrySet;
			}
		}

		public Collection<V> values() {
			synchronized (mutex) {
				if (values==null)
					values = new SynchronizedCollection<>(m.values(), mutex);
				return values;
			}
		}

		public boolean equals(Object o) {
			if (this == o)
				return true;
			synchronized (mutex) {return m.equals(o);}
		}
		public int hashCode() {
			synchronized (mutex) {return m.hashCode();}
		}
		public String toString() {
			synchronized (mutex) {return m.toString();}
		}

		// Override default methods in Map
		@Override
		public V getOrDefault(Object k, V defaultValue) {
			synchronized (mutex) {return m.getOrDefault(k, defaultValue);}
		}
		@Override
		public void forEach(BiConsumer<? super K, ? super V> action) {
			synchronized (mutex) {m.forEach(action);}
		}
		@Override
		public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
			synchronized (mutex) {m.replaceAll(function);}
		}
		@Override
		public V putIfAbsent(K key, V value) {
			synchronized (mutex) {return m.putIfAbsent(key, value);}
		}
		@Override
		public boolean remove(Object key, Object value) {
			synchronized (mutex) {return m.remove(key, value);}
		}
		@Override
		public boolean replace(K key, V oldValue, V newValue) {
			synchronized (mutex) {return m.replace(key, oldValue, newValue);}
		}
		@Override
		public V replace(K key, V value) {
			synchronized (mutex) {return m.replace(key, value);}
		}
		@Override
		public V computeIfAbsent(K key,
		                         Function<? super K, ? extends V> mappingFunction) {
			synchronized (mutex) {return m.computeIfAbsent(key, mappingFunction);}
		}
		@Override
		public V computeIfPresent(K key,
		                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			synchronized (mutex) {return m.computeIfPresent(key, remappingFunction);}
		}
		@Override
		public V compute(K key,
		                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			synchronized (mutex) {return m.compute(key, remappingFunction);}
		}
		@Override
		public V merge(K key, V value,
		               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
			synchronized (mutex) {return m.merge(key, value, remappingFunction);}
		}

		private void writeObject(ObjectOutputStream s) throws IOException {
			synchronized (mutex) {s.defaultWriteObject();}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) sorted map backed by the specified
	 * sorted map.  In order to guarantee serial access, it is critical that
	 * <strong>all</strong> access to the backing sorted map is accomplished
	 * through the returned sorted map (or its views).<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * sorted map when iterating over any of its collection views, or the
	 * collections views of any of its <tt>subMap</tt>, <tt>headMap</tt> or
	 * <tt>tailMap</tt> views.
	 * <pre>
	 *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
	 *      ...
	 *  Set s = m.keySet();  // Needn't be in synchronized block
	 *      ...
	 *  synchronized (m) {  // Synchronizing on m, not s!
	 *      Iterator i = s.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * or:
	 * <pre>
	 *  SortedMap m = Collections.synchronizedSortedMap(new TreeMap());
	 *  SortedMap m2 = m.subMap(foo, bar);
	 *      ...
	 *  Set s2 = m2.keySet();  // Needn't be in synchronized block
	 *      ...
	 *  synchronized (m) {  // Synchronizing on m, not m2 or s2!
	 *      Iterator i = s.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned sorted map will be serializable if the specified
	 * sorted map is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param  m the sorted map to be "wrapped" in a synchronized sorted map.
	 * @return a synchronized view of the specified sorted map.
	 */
	public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
		return new SynchronizedSortedMap<>(m);
	}

	/**
	 * @serial include
	 */
	static class SynchronizedSortedMap<K,V>
			extends SynchronizedMap<K,V>
			implements SortedMap<K,V>
	{
		private static final long serialVersionUID = -8798146769416483793L;

		private final SortedMap<K,V> sm;

		SynchronizedSortedMap(SortedMap<K,V> m) {
			super(m);
			sm = m;
		}
		SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
			super(m, mutex);
			sm = m;
		}

		public Comparator<? super K> comparator() {
			synchronized (mutex) {return sm.comparator();}
		}

		public SortedMap<K,V> subMap(K fromKey, K toKey) {
			synchronized (mutex) {
				return new SynchronizedSortedMap<>(
						sm.subMap(fromKey, toKey), mutex);
			}
		}
		public SortedMap<K,V> headMap(K toKey) {
			synchronized (mutex) {
				return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex);
			}
		}
		public SortedMap<K,V> tailMap(K fromKey) {
			synchronized (mutex) {
				return new SynchronizedSortedMap<>(sm.tailMap(fromKey),mutex);
			}
		}

		public K firstKey() {
			synchronized (mutex) {return sm.firstKey();}
		}
		public K lastKey() {
			synchronized (mutex) {return sm.lastKey();}
		}
	}

	/**
	 * Returns a synchronized (thread-safe) navigable map backed by the
	 * specified navigable map.  In order to guarantee serial access, it is
	 * critical that <strong>all</strong> access to the backing navigable map is
	 * accomplished through the returned navigable map (or its views).<p>
	 *
	 * It is imperative that the user manually synchronize on the returned
	 * navigable map when iterating over any of its collection views, or the
	 * collections views of any of its {@code subMap}, {@code headMap} or
	 * {@code tailMap} views.
	 * <pre>
	 *  NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());
	 *      ...
	 *  Set s = m.keySet();  // Needn't be in synchronized block
	 *      ...
	 *  synchronized (m) {  // Synchronizing on m, not s!
	 *      Iterator i = s.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * or:
	 * <pre>
	 *  NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap());
	 *  NavigableMap m2 = m.subMap(foo, true, bar, false);
	 *      ...
	 *  Set s2 = m2.keySet();  // Needn't be in synchronized block
	 *      ...
	 *  synchronized (m) {  // Synchronizing on m, not m2 or s2!
	 *      Iterator i = s.iterator(); // Must be in synchronized block
	 *      while (i.hasNext())
	 *          foo(i.next());
	 *  }
	 * </pre>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>The returned navigable map will be serializable if the specified
	 * navigable map is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param  m the navigable map to be "wrapped" in a synchronized navigable
	 *              map
	 * @return a synchronized view of the specified navigable map.
	 * @since 1.8
	 */
	public static <K,V> NavigableMap<K,V> synchronizedNavigableMap(NavigableMap<K,V> m) {
		return new SynchronizedNavigableMap<>(m);
	}

	/**
	 * A synchronized NavigableMap.
	 *
	 * @serial include
	 */
	static class SynchronizedNavigableMap<K,V>
			extends SynchronizedSortedMap<K,V>
			implements NavigableMap<K,V>
	{
		private static final long serialVersionUID = 699392247599746807L;

		private final NavigableMap<K,V> nm;

		SynchronizedNavigableMap(NavigableMap<K,V> m) {
			super(m);
			nm = m;
		}
		SynchronizedNavigableMap(NavigableMap<K,V> m, Object mutex) {
			super(m, mutex);
			nm = m;
		}

		public Entry<K, V> lowerEntry(K key)
		{ synchronized (mutex) { return nm.lowerEntry(key); } }
		public K lowerKey(K key)
		{ synchronized (mutex) { return nm.lowerKey(key); } }
		public Entry<K, V> floorEntry(K key)
		{ synchronized (mutex) { return nm.floorEntry(key); } }
		public K floorKey(K key)
		{ synchronized (mutex) { return nm.floorKey(key); } }
		public Entry<K, V> ceilingEntry(K key)
		{ synchronized (mutex) { return nm.ceilingEntry(key); } }
		public K ceilingKey(K key)
		{ synchronized (mutex) { return nm.ceilingKey(key); } }
		public Entry<K, V> higherEntry(K key)
		{ synchronized (mutex) { return nm.higherEntry(key); } }
		public K higherKey(K key)
		{ synchronized (mutex) { return nm.higherKey(key); } }
		public Entry<K, V> firstEntry()
		{ synchronized (mutex) { return nm.firstEntry(); } }
		public Entry<K, V> lastEntry()
		{ synchronized (mutex) { return nm.lastEntry(); } }
		public Entry<K, V> pollFirstEntry()
		{ synchronized (mutex) { return nm.pollFirstEntry(); } }
		public Entry<K, V> pollLastEntry()
		{ synchronized (mutex) { return nm.pollLastEntry(); } }

		public NavigableMap<K, V> descendingMap() {
			synchronized (mutex) {
				return
						new SynchronizedNavigableMap<>(nm.descendingMap(), mutex);
			}
		}

		public NavigableSet<K> keySet() {
			return navigableKeySet();
		}

		public NavigableSet<K> navigableKeySet() {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex);
			}
		}

		public NavigableSet<K> descendingKeySet() {
			synchronized (mutex) {
				return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex);
			}
		}


		public SortedMap<K,V> subMap(K fromKey, K toKey) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(
						nm.subMap(fromKey, true, toKey, false), mutex);
			}
		}
		public SortedMap<K,V> headMap(K toKey) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex);
			}
		}
		public SortedMap<K,V> tailMap(K fromKey) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true),mutex);
			}
		}

		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(
						nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex);
			}
		}

		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(
						nm.headMap(toKey, inclusive), mutex);
			}
		}

		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			synchronized (mutex) {
				return new SynchronizedNavigableMap<>(
						nm.tailMap(fromKey, inclusive), mutex);
			}
		}
	}

	// Dynamically typesafe collection wrappers

	/**
	 * Returns a dynamically typesafe view of the specified collection.
	 * Any attempt to insert an element of the wrong type will result in an
	 * immediate {@link ClassCastException}.  Assuming a collection
	 * contains no incorrectly typed elements prior to the time a
	 * dynamically typesafe view is generated, and that all subsequent
	 * access to the collection takes place through the view, it is
	 * <i>guaranteed</i> that the collection cannot contain an incorrectly
	 * typed element.
	 *
	 * <p>The generics mechanism in the language provides compile-time
	 * (static) type checking, but it is possible to defeat this mechanism
	 * with unchecked casts.  Usually this is not a problem, as the compiler
	 * issues warnings on all such unchecked operations.  There are, however,
	 * times when static type checking alone is not sufficient.  For example,
	 * suppose a collection is passed to a third-party library and it is
	 * imperative that the library code not corrupt the collection by
	 * inserting an element of the wrong type.
	 *
	 * <p>Another use of dynamically typesafe views is debugging.  Suppose a
	 * program fails with a {@code ClassCastException}, indicating that an
	 * incorrectly typed element was put into a parameterized collection.
	 * Unfortunately, the exception can occur at any time after the erroneous
	 * element is inserted, so it typically provides little or no information
	 * as to the real source of the problem.  If the problem is reproducible,
	 * one can quickly determine its source by temporarily modifying the
	 * program to wrap the collection with a dynamically typesafe view.
	 * For example, this declaration:
	 *  <pre> {@code
	 *     Collection<String> c = new HashSet<>();
	 * }</pre>
	 * may be replaced temporarily by this one:
	 *  <pre> {@code
	 *     Collection<String> c = Collections.checkedCollection(
	 *         new HashSet<>(), String.class);
	 * }</pre>
	 * Running the program again will cause it to fail at the point where
	 * an incorrectly typed element is inserted into the collection, clearly
	 * identifying the source of the problem.  Once the problem is fixed, the
	 * modified declaration may be reverted back to the original.
	 *
	 * <p>The returned collection does <i>not</i> pass the hashCode and equals
	 * operations through to the backing collection, but relies on
	 * {@code Object}'s {@code equals} and {@code hashCode} methods.  This
	 * is necessary to preserve the contracts of these operations in the case
	 * that the backing collection is a set or a list.
	 *
	 * <p>The returned collection will be serializable if the specified
	 * collection is serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned collection permits insertion of null elements
	 * whenever the backing collection does.
	 *
	 * @param <E> the class of the objects in the collection
	 * @param c the collection for which a dynamically typesafe view is to be
	 *          returned
	 * @param type the type of element that {@code c} is permitted to hold
	 * @return a dynamically typesafe view of the specified collection
	 * @since 1.5
	 */
	public static <E> Collection<E> checkedCollection(Collection<E> c,
	                                                  Class<E> type) {
		return new CheckedCollection<>(c, type);
	}

	@SuppressWarnings("unchecked")
	static <T> T[] zeroLengthArray(Class<T> type) {
		return (T[]) Array.newInstance(type, 0);
	}

	/**
	 * @serial include
	 */
	static class CheckedCollection<E> implements Collection<E>, Serializable {
		private static final long serialVersionUID = 1578914078182001775L;

		final Collection<E> c;
		final Class<E> type;

		@SuppressWarnings("unchecked")
		E typeCheck(Object o) {
			if (o != null && !type.isInstance(o))
				throw new ClassCastException(badElementMsg(o));
			return (E) o;
		}

		private String badElementMsg(Object o) {
			return "Attempt to insert " + o.getClass() +
					" element into collection with element type " + type;
		}

		CheckedCollection(Collection<E> c, Class<E> type) {
			this.c = Objects.requireNonNull(c, "c");
			this.type = Objects.requireNonNull(type, "type");
		}

		public int size()                 { return c.size(); }
		public boolean isEmpty()          { return c.isEmpty(); }
		public boolean contains(Object o) { return c.contains(o); }
		public Object[] toArray()         { return c.toArray(); }
		public <T> T[] toArray(T[] a)     { return c.toArray(a); }
		public String toString()          { return c.toString(); }
		public boolean remove(Object o)   { return c.remove(o); }
		public void clear()               {        c.clear(); }

		public boolean containsAll(Collection<?> coll) {
			return c.containsAll(coll);
		}
		public boolean removeAll(Collection<?> coll) {
			return c.removeAll(coll);
		}
		public boolean retainAll(Collection<?> coll) {
			return c.retainAll(coll);
		}

		public Iterator<E> iterator() {
			// JDK-6363904 - unwrapped iterator could be typecast to
			// ListIterator with unsafe set()
			final Iterator<E> it = c.iterator();
			return new Iterator<E>() {
				public boolean hasNext() { return it.hasNext(); }
				public E next()          { return it.next(); }
				public void remove()     {        it.remove(); }};
		}

		public boolean add(E e)          { return c.add(typeCheck(e)); }

		private E[] zeroLengthElementArray; // Lazily initialized

		private E[] zeroLengthElementArray() {
			return zeroLengthElementArray != null ? zeroLengthElementArray :
					(zeroLengthElementArray = zeroLengthArray(type));
		}

		@SuppressWarnings("unchecked")
		Collection<E> checkedCopyOf(Collection<? extends E> coll) {
			Object[] a;
			try {
				E[] z = zeroLengthElementArray();
				a = coll.toArray(z);
				// Defend against coll violating the toArray contract
				if (a.getClass() != z.getClass())
					a = Arrays.copyOf(a, a.length, z.getClass());
			} catch (ArrayStoreException ignore) {
				// To get better and consistent diagnostics,
				// we call typeCheck explicitly on each element.
				// We call clone() to defend against coll retaining a
				// reference to the returned array and storing a bad
				// element into it after it has been type checked.
				a = coll.toArray().clone();
				for (Object o : a)
					typeCheck(o);
			}
			// A slight abuse of the type system, but safe here.
			return (Collection<E>) Arrays.asList(a);
		}

		public boolean addAll(Collection<? extends E> coll) {
			// Doing things this way insulates us from concurrent changes
			// in the contents of coll and provides all-or-nothing
			// semantics (which we wouldn't get if we type-checked each
			// element as we added it)
			return c.addAll(checkedCopyOf(coll));
		}

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {c.forEach(action);}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			return c.removeIf(filter);
		}
		@Override
		public Spliterator<E> spliterator() {return c.spliterator();}
		@Override
		public Stream<E> stream()           {return c.stream();}
		@Override
		public Stream<E> parallelStream()   {return c.parallelStream();}
	}

	/**
	 * Returns a dynamically typesafe view of the specified queue.
	 * Any attempt to insert an element of the wrong type will result in
	 * an immediate {@link ClassCastException}.  Assuming a queue contains
	 * no incorrectly typed elements prior to the time a dynamically typesafe
	 * view is generated, and that all subsequent access to the queue
	 * takes place through the view, it is <i>guaranteed</i> that the
	 * queue cannot contain an incorrectly typed element.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned queue will be serializable if the specified queue
	 * is serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned queue permits insertion of {@code null} elements
	 * whenever the backing queue does.
	 *
	 * @param <E> the class of the objects in the queue
	 * @param queue the queue for which a dynamically typesafe view is to be
	 *             returned
	 * @param type the type of element that {@code queue} is permitted to hold
	 * @return a dynamically typesafe view of the specified queue
	 * @since 1.8
	 */
	public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) {
		return new CheckedQueue<>(queue, type);
	}

	/**
	 * @serial include
	 */
	static class CheckedQueue<E>
			extends CheckedCollection<E>
			implements Queue<E>, Serializable
	{
		private static final long serialVersionUID = 1433151992604707767L;
		final Queue<E> queue;

		CheckedQueue(Queue<E> queue, Class<E> elementType) {
			super(queue, elementType);
			this.queue = queue;
		}

		public E element()              {return queue.element();}
		public boolean equals(Object o) {return o == this || c.equals(o);}
		public int hashCode()           {return c.hashCode();}
		public E peek()                 {return queue.peek();}
		public E poll()                 {return queue.poll();}
		public E remove()               {return queue.remove();}
		public boolean offer(E e)       {return queue.offer(typeCheck(e));}
	}

	/**
	 * Returns a dynamically typesafe view of the specified set.
	 * Any attempt to insert an element of the wrong type will result in
	 * an immediate {@link ClassCastException}.  Assuming a set contains
	 * no incorrectly typed elements prior to the time a dynamically typesafe
	 * view is generated, and that all subsequent access to the set
	 * takes place through the view, it is <i>guaranteed</i> that the
	 * set cannot contain an incorrectly typed element.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned set will be serializable if the specified set is
	 * serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned set permits insertion of null elements whenever
	 * the backing set does.
	 *
	 * @param <E> the class of the objects in the set
	 * @param s the set for which a dynamically typesafe view is to be
	 *          returned
	 * @param type the type of element that {@code s} is permitted to hold
	 * @return a dynamically typesafe view of the specified set
	 * @since 1.5
	 */
	public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
		return new CheckedSet<>(s, type);
	}

	/**
	 * @serial include
	 */
	static class CheckedSet<E> extends CheckedCollection<E>
			implements Set<E>, Serializable
	{
		private static final long serialVersionUID = 4694047833775013803L;

		CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }

		public boolean equals(Object o) { return o == this || c.equals(o); }
		public int hashCode()           { return c.hashCode(); }
	}

	/**
	 * Returns a dynamically typesafe view of the specified sorted set.
	 * Any attempt to insert an element of the wrong type will result in an
	 * immediate {@link ClassCastException}.  Assuming a sorted set
	 * contains no incorrectly typed elements prior to the time a
	 * dynamically typesafe view is generated, and that all subsequent
	 * access to the sorted set takes place through the view, it is
	 * <i>guaranteed</i> that the sorted set cannot contain an incorrectly
	 * typed element.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned sorted set will be serializable if the specified sorted
	 * set is serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned sorted set permits insertion of null elements
	 * whenever the backing sorted set does.
	 *
	 * @param <E> the class of the objects in the set
	 * @param s the sorted set for which a dynamically typesafe view is to be
	 *          returned
	 * @param type the type of element that {@code s} is permitted to hold
	 * @return a dynamically typesafe view of the specified sorted set
	 * @since 1.5
	 */
	public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,
	                                                Class<E> type) {
		return new CheckedSortedSet<>(s, type);
	}

	/**
	 * @serial include
	 */
	static class CheckedSortedSet<E> extends CheckedSet<E>
			implements SortedSet<E>, Serializable
	{
		private static final long serialVersionUID = 1599911165492914959L;

		private final SortedSet<E> ss;

		CheckedSortedSet(SortedSet<E> s, Class<E> type) {
			super(s, type);
			ss = s;
		}

		public Comparator<? super E> comparator() { return ss.comparator(); }
		public E first()                   { return ss.first(); }
		public E last()                    { return ss.last(); }

		public SortedSet<E> subSet(E fromElement, E toElement) {
			return checkedSortedSet(ss.subSet(fromElement,toElement), type);
		}
		public SortedSet<E> headSet(E toElement) {
			return checkedSortedSet(ss.headSet(toElement), type);
		}
		public SortedSet<E> tailSet(E fromElement) {
			return checkedSortedSet(ss.tailSet(fromElement), type);
		}
	}

	/**
	 * Returns a dynamically typesafe view of the specified navigable set.
	 * Any attempt to insert an element of the wrong type will result in an
	 * immediate {@link ClassCastException}.  Assuming a navigable set
	 * contains no incorrectly typed elements prior to the time a
	 * dynamically typesafe view is generated, and that all subsequent
	 * access to the navigable set takes place through the view, it is
	 * <em>guaranteed</em> that the navigable set cannot contain an incorrectly
	 * typed element.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned navigable set will be serializable if the specified
	 * navigable set is serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned navigable set permits insertion of null elements
	 * whenever the backing sorted set does.
	 *
	 * @param <E> the class of the objects in the set
	 * @param s the navigable set for which a dynamically typesafe view is to be
	 *          returned
	 * @param type the type of element that {@code s} is permitted to hold
	 * @return a dynamically typesafe view of the specified navigable set
	 * @since 1.8
	 */
	public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s,
	                                                      Class<E> type) {
		return new CheckedNavigableSet<>(s, type);
	}

	/**
	 * @serial include
	 */
	static class CheckedNavigableSet<E> extends CheckedSortedSet<E>
			implements NavigableSet<E>, Serializable
	{
		private static final long serialVersionUID = -5429120189805438922L;

		private final NavigableSet<E> ns;

		CheckedNavigableSet(NavigableSet<E> s, Class<E> type) {
			super(s, type);
			ns = s;
		}

		public E lower(E e)                             { return ns.lower(e); }
		public E floor(E e)                             { return ns.floor(e); }
		public E ceiling(E e)                         { return ns.ceiling(e); }
		public E higher(E e)                           { return ns.higher(e); }
		public E pollFirst()                         { return ns.pollFirst(); }
		public E pollLast()                            {return ns.pollLast(); }
		public NavigableSet<E> descendingSet()
		{ return checkedNavigableSet(ns.descendingSet(), type); }
		public Iterator<E> descendingIterator()
		{return checkedNavigableSet(ns.descendingSet(), type).iterator(); }

		public NavigableSet<E> subSet(E fromElement, E toElement) {
			return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type);
		}
		public NavigableSet<E> headSet(E toElement) {
			return checkedNavigableSet(ns.headSet(toElement, false), type);
		}
		public NavigableSet<E> tailSet(E fromElement) {
			return checkedNavigableSet(ns.tailSet(fromElement, true), type);
		}

		public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
			return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type);
		}

		public NavigableSet<E> headSet(E toElement, boolean inclusive) {
			return checkedNavigableSet(ns.headSet(toElement, inclusive), type);
		}

		public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
			return checkedNavigableSet(ns.tailSet(fromElement, inclusive), type);
		}
	}

	/**
	 * Returns a dynamically typesafe view of the specified list.
	 * Any attempt to insert an element of the wrong type will result in
	 * an immediate {@link ClassCastException}.  Assuming a list contains
	 * no incorrectly typed elements prior to the time a dynamically typesafe
	 * view is generated, and that all subsequent access to the list
	 * takes place through the view, it is <i>guaranteed</i> that the
	 * list cannot contain an incorrectly typed element.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned list will be serializable if the specified list
	 * is serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned list permits insertion of null elements whenever
	 * the backing list does.
	 *
	 * @param <E> the class of the objects in the list
	 * @param list the list for which a dynamically typesafe view is to be
	 *             returned
	 * @param type the type of element that {@code list} is permitted to hold
	 * @return a dynamically typesafe view of the specified list
	 * @since 1.5
	 */
	public static <E> List<E> checkedList(List<E> list, Class<E> type) {
		return (list instanceof RandomAccess ?
				new CheckedRandomAccessList<>(list, type) :
				new CheckedList<>(list, type));
	}

	/**
	 * @serial include
	 */
	static class CheckedList<E>
			extends CheckedCollection<E>
			implements List<E>
	{
		private static final long serialVersionUID = 65247728283967356L;
		final List<E> list;

		CheckedList(List<E> list, Class<E> type) {
			super(list, type);
			this.list = list;
		}

		public boolean equals(Object o)  { return o == this || list.equals(o); }
		public int hashCode()            { return list.hashCode(); }
		public E get(int index)          { return list.get(index); }
		public E remove(int index)       { return list.remove(index); }
		public int indexOf(Object o)     { return list.indexOf(o); }
		public int lastIndexOf(Object o) { return list.lastIndexOf(o); }

		public E set(int index, E element) {
			return list.set(index, typeCheck(element));
		}

		public void add(int index, E element) {
			list.add(index, typeCheck(element));
		}

		public boolean addAll(int index, Collection<? extends E> c) {
			return list.addAll(index, checkedCopyOf(c));
		}
		public ListIterator<E> listIterator()   { return listIterator(0); }

		public ListIterator<E> listIterator(final int index) {
			final ListIterator<E> i = list.listIterator(index);

			return new ListIterator<E>() {
				public boolean hasNext()     { return i.hasNext(); }
				public E next()              { return i.next(); }
				public boolean hasPrevious() { return i.hasPrevious(); }
				public E previous()          { return i.previous(); }
				public int nextIndex()       { return i.nextIndex(); }
				public int previousIndex()   { return i.previousIndex(); }
				public void remove()         {        i.remove(); }

				public void set(E e) {
					i.set(typeCheck(e));
				}

				public void add(E e) {
					i.add(typeCheck(e));
				}

				@Override
				public void forEachRemaining(Consumer<? super E> action) {
					i.forEachRemaining(action);
				}
			};
		}

		public List<E> subList(int fromIndex, int toIndex) {
			return new CheckedList<>(list.subList(fromIndex, toIndex), type);
		}

		/**
		 * {@inheritDoc}
		 *
		 * @throws ClassCastException if the class of an element returned by the
		 *         operator prevents it from being added to this collection. The
		 *         exception may be thrown after some elements of the list have
		 *         already been replaced.
		 */
		@Override
		public void replaceAll(UnaryOperator<E> operator) {
			Objects.requireNonNull(operator);
			list.replaceAll(e -> typeCheck(operator.apply(e)));
		}

		@Override
		public void sort(Comparator<? super E> c) {
			list.sort(c);
		}
	}

	/**
	 * @serial include
	 */
	static class CheckedRandomAccessList<E> extends CheckedList<E>
			implements RandomAccess
	{
		private static final long serialVersionUID = 1638200125423088369L;

		CheckedRandomAccessList(List<E> list, Class<E> type) {
			super(list, type);
		}

		public List<E> subList(int fromIndex, int toIndex) {
			return new CheckedRandomAccessList<>(
					list.subList(fromIndex, toIndex), type);
		}
	}

	/**
	 * Returns a dynamically typesafe view of the specified map.
	 * Any attempt to insert a mapping whose key or value have the wrong
	 * type will result in an immediate {@link ClassCastException}.
	 * Similarly, any attempt to modify the value currently associated with
	 * a key will result in an immediate {@link ClassCastException},
	 * whether the modification is attempted directly through the map
	 * itself, or through a {@link Map.Entry} instance obtained from the
	 * map's {@link Map#entrySet() entry set} view.
	 *
	 * <p>Assuming a map contains no incorrectly typed keys or values
	 * prior to the time a dynamically typesafe view is generated, and
	 * that all subsequent access to the map takes place through the view
	 * (or one of its collection views), it is <i>guaranteed</i> that the
	 * map cannot contain an incorrectly typed key or value.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned map will be serializable if the specified map is
	 * serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned map permits insertion of null keys or values
	 * whenever the backing map does.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param m the map for which a dynamically typesafe view is to be
	 *          returned
	 * @param keyType the type of key that {@code m} is permitted to hold
	 * @param valueType the type of value that {@code m} is permitted to hold
	 * @return a dynamically typesafe view of the specified map
	 * @since 1.5
	 */
	public static <K, V> Map<K, V> checkedMap(Map<K, V> m,
	                                          Class<K> keyType,
	                                          Class<V> valueType) {
		return new CheckedMap<>(m, keyType, valueType);
	}


	/**
	 * @serial include
	 */
	private static class CheckedMap<K,V>
			implements Map<K,V>, Serializable
	{
		private static final long serialVersionUID = 5742860141034234728L;

		private final Map<K, V> m;
		final Class<K> keyType;
		final Class<V> valueType;

		private void typeCheck(Object key, Object value) {
			if (key != null && !keyType.isInstance(key))
				throw new ClassCastException(badKeyMsg(key));

			if (value != null && !valueType.isInstance(value))
				throw new ClassCastException(badValueMsg(value));
		}

		private BiFunction<? super K, ? super V, ? extends V> typeCheck(
				BiFunction<? super K, ? super V, ? extends V> func) {
			Objects.requireNonNull(func);
			return (k, v) -> {
				V newValue = func.apply(k, v);
				typeCheck(k, newValue);
				return newValue;
			};
		}

		private String badKeyMsg(Object key) {
			return "Attempt to insert " + key.getClass() +
					" key into map with key type " + keyType;
		}

		private String badValueMsg(Object value) {
			return "Attempt to insert " + value.getClass() +
					" value into map with value type " + valueType;
		}

		CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
			this.m = Objects.requireNonNull(m);
			this.keyType = Objects.requireNonNull(keyType);
			this.valueType = Objects.requireNonNull(valueType);
		}

		public int size()                      { return m.size(); }
		public boolean isEmpty()               { return m.isEmpty(); }
		public boolean containsKey(Object key) { return m.containsKey(key); }
		public boolean containsValue(Object v) { return m.containsValue(v); }
		public V get(Object key)               { return m.get(key); }
		public V remove(Object key)            { return m.remove(key); }
		public void clear()                    { m.clear(); }
		public Set<K> keySet()                 { return m.keySet(); }
		public Collection<V> values()          { return m.values(); }
		public boolean equals(Object o)        { return o == this || m.equals(o); }
		public int hashCode()                  { return m.hashCode(); }
		public String toString()               { return m.toString(); }

		public V put(K key, V value) {
			typeCheck(key, value);
			return m.put(key, value);
		}

		@SuppressWarnings("unchecked")
		public void putAll(Map<? extends K, ? extends V> t) {
			// Satisfy the following goals:
			// - good diagnostics in case of type mismatch
			// - all-or-nothing semantics
			// - protection from malicious t
			// - correct behavior if t is a concurrent map
			Object[] entries = t.entrySet().toArray();
			List<Map.Entry<K,V>> checked = new ArrayList<>(entries.length);
			for (Object o : entries) {
				Map.Entry<?,?> e = (Map.Entry<?,?>) o;
				Object k = e.getKey();
				Object v = e.getValue();
				typeCheck(k, v);
				checked.add(
						new AbstractMap.SimpleImmutableEntry<>((K)k, (V)v));
			}
			for (Map.Entry<K,V> e : checked)
				m.put(e.getKey(), e.getValue());
		}

		private transient Set<Map.Entry<K,V>> entrySet;

		public Set<Map.Entry<K,V>> entrySet() {
			if (entrySet==null)
				entrySet = new CheckedEntrySet<>(m.entrySet(), valueType);
			return entrySet;
		}

		// Override default methods in Map
		@Override
		public void forEach(BiConsumer<? super K, ? super V> action) {
			m.forEach(action);
		}

		@Override
		public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
			m.replaceAll(typeCheck(function));
		}

		@Override
		public V putIfAbsent(K key, V value) {
			typeCheck(key, value);
			return m.putIfAbsent(key, value);
		}

		@Override
		public boolean remove(Object key, Object value) {
			return m.remove(key, value);
		}

		@Override
		public boolean replace(K key, V oldValue, V newValue) {
			typeCheck(key, newValue);
			return m.replace(key, oldValue, newValue);
		}

		@Override
		public V replace(K key, V value) {
			typeCheck(key, value);
			return m.replace(key, value);
		}

		@Override
		public V computeIfAbsent(K key,
		                         Function<? super K, ? extends V> mappingFunction) {
			Objects.requireNonNull(mappingFunction);
			return m.computeIfAbsent(key, k -> {
				V value = mappingFunction.apply(k);
				typeCheck(k, value);
				return value;
			});
		}

		@Override
		public V computeIfPresent(K key,
		                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			return m.computeIfPresent(key, typeCheck(remappingFunction));
		}

		@Override
		public V compute(K key,
		                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			return m.compute(key, typeCheck(remappingFunction));
		}

		@Override
		public V merge(K key, V value,
		               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
			Objects.requireNonNull(remappingFunction);
			return m.merge(key, value, (v1, v2) -> {
				V newValue = remappingFunction.apply(v1, v2);
				typeCheck(null, newValue);
				return newValue;
			});
		}

		/**
		 * We need this class in addition to CheckedSet as Map.Entry permits
		 * modification of the backing Map via the setValue operation.  This
		 * class is subtle: there are many possible attacks that must be
		 * thwarted.
		 *
		 * @serial exclude
		 */
		static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
			private final Set<Map.Entry<K,V>> s;
			private final Class<V> valueType;

			CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
				this.s = s;
				this.valueType = valueType;
			}

			public int size()        { return s.size(); }
			public boolean isEmpty() { return s.isEmpty(); }
			public String toString() { return s.toString(); }
			public int hashCode()    { return s.hashCode(); }
			public void clear()      {        s.clear(); }

			public boolean add(Map.Entry<K, V> e) {
				throw new UnsupportedOperationException();
			}
			public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
				throw new UnsupportedOperationException();
			}

			public Iterator<Map.Entry<K,V>> iterator() {
				final Iterator<Map.Entry<K, V>> i = s.iterator();
				final Class<V> valueType = this.valueType;

				return new Iterator<Map.Entry<K,V>>() {
					public boolean hasNext() { return i.hasNext(); }
					public void remove()     { i.remove(); }

					public Map.Entry<K,V> next() {
						return checkedEntry(i.next(), valueType);
					}
				};
			}

			@SuppressWarnings("unchecked")
			public Object[] toArray() {
				Object[] source = s.toArray();

				/*
				 * Ensure that we don't get an ArrayStoreException even if
				 * s.toArray returns an array of something other than Object
				 */
				Object[] dest = (CheckedEntry.class.isInstance(
						source.getClass().getComponentType()) ? source :
						new Object[source.length]);

				for (int i = 0; i < source.length; i++)
					dest[i] = checkedEntry((Map.Entry<K,V>)source[i],
							valueType);
				return dest;
			}

			@SuppressWarnings("unchecked")
			public <T> T[] toArray(T[] a) {
				// We don't pass a to s.toArray, to avoid window of
				// vulnerability wherein an unscrupulous multithreaded client
				// could get his hands on raw (unwrapped) Entries from s.
				T[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));

				for (int i=0; i<arr.length; i++)
					arr[i] = (T) checkedEntry((Map.Entry<K,V>)arr[i],
							valueType);
				if (arr.length > a.length)
					return arr;

				System.arraycopy(arr, 0, a, 0, arr.length);
				if (a.length > arr.length)
					a[arr.length] = null;
				return a;
			}

			/**
			 * This method is overridden to protect the backing set against
			 * an object with a nefarious equals function that senses
			 * that the equality-candidate is Map.Entry and calls its
			 * setValue method.
			 */
			public boolean contains(Object o) {
				if (!(o instanceof Map.Entry))
					return false;
				Map.Entry<?,?> e = (Map.Entry<?,?>) o;
				return s.contains(
						(e instanceof CheckedEntry) ? e : checkedEntry(e, valueType));
			}

			/**
			 * The bulk collection methods are overridden to protect
			 * against an unscrupulous collection whose contains(Object o)
			 * method senses when o is a Map.Entry, and calls o.setValue.
			 */
			public boolean containsAll(Collection<?> c) {
				for (Object o : c)
					if (!contains(o)) // Invokes safe contains() above
						return false;
				return true;
			}

			public boolean remove(Object o) {
				if (!(o instanceof Map.Entry))
					return false;
				return s.remove(new AbstractMap.SimpleImmutableEntry
						<>((Map.Entry<?,?>)o));
			}

			public boolean removeAll(Collection<?> c) {
				return batchRemove(c, false);
			}
			public boolean retainAll(Collection<?> c) {
				return batchRemove(c, true);
			}
			private boolean batchRemove(Collection<?> c, boolean complement) {
				Objects.requireNonNull(c);
				boolean modified = false;
				Iterator<Map.Entry<K,V>> it = iterator();
				while (it.hasNext()) {
					if (c.contains(it.next()) != complement) {
						it.remove();
						modified = true;
					}
				}
				return modified;
			}

			public boolean equals(Object o) {
				if (o == this)
					return true;
				if (!(o instanceof Set))
					return false;
				Set<?> that = (Set<?>) o;
				return that.size() == s.size()
						&& containsAll(that); // Invokes safe containsAll() above
			}

			static <K,V,T> CheckedEntry<K,V,T> checkedEntry(Map.Entry<K,V> e,
			                                                Class<T> valueType) {
				return new CheckedEntry<>(e, valueType);
			}

			/**
			 * This "wrapper class" serves two purposes: it prevents
			 * the client from modifying the backing Map, by short-circuiting
			 * the setValue method, and it protects the backing Map against
			 * an ill-behaved Map.Entry that attempts to modify another
			 * Map.Entry when asked to perform an equality check.
			 */
			private static class CheckedEntry<K,V,T> implements Map.Entry<K,V> {
				private final Map.Entry<K, V> e;
				private final Class<T> valueType;

				CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) {
					this.e = Objects.requireNonNull(e);
					this.valueType = Objects.requireNonNull(valueType);
				}

				public K getKey()        { return e.getKey(); }
				public V getValue()      { return e.getValue(); }
				public int hashCode()    { return e.hashCode(); }
				public String toString() { return e.toString(); }

				public V setValue(V value) {
					if (value != null && !valueType.isInstance(value))
						throw new ClassCastException(badValueMsg(value));
					return e.setValue(value);
				}

				private String badValueMsg(Object value) {
					return "Attempt to insert " + value.getClass() +
							" value into map with value type " + valueType;
				}

				public boolean equals(Object o) {
					if (o == this)
						return true;
					if (!(o instanceof Map.Entry))
						return false;
					return e.equals(new AbstractMap.SimpleImmutableEntry
							<>((Map.Entry<?,?>)o));
				}
			}
		}
	}

	/**
	 * Returns a dynamically typesafe view of the specified sorted map.
	 * Any attempt to insert a mapping whose key or value have the wrong
	 * type will result in an immediate {@link ClassCastException}.
	 * Similarly, any attempt to modify the value currently associated with
	 * a key will result in an immediate {@link ClassCastException},
	 * whether the modification is attempted directly through the map
	 * itself, or through a {@link Map.Entry} instance obtained from the
	 * map's {@link Map#entrySet() entry set} view.
	 *
	 * <p>Assuming a map contains no incorrectly typed keys or values
	 * prior to the time a dynamically typesafe view is generated, and
	 * that all subsequent access to the map takes place through the view
	 * (or one of its collection views), it is <i>guaranteed</i> that the
	 * map cannot contain an incorrectly typed key or value.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned map will be serializable if the specified map is
	 * serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned map permits insertion of null keys or values
	 * whenever the backing map does.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param m the map for which a dynamically typesafe view is to be
	 *          returned
	 * @param keyType the type of key that {@code m} is permitted to hold
	 * @param valueType the type of value that {@code m} is permitted to hold
	 * @return a dynamically typesafe view of the specified map
	 * @since 1.5
	 */
	public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
	                                                    Class<K> keyType,
	                                                    Class<V> valueType) {
		return new CheckedSortedMap<>(m, keyType, valueType);
	}

	/**
	 * @serial include
	 */
	static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
			implements SortedMap<K,V>, Serializable
	{
		private static final long serialVersionUID = 1599671320688067438L;

		private final SortedMap<K, V> sm;

		CheckedSortedMap(SortedMap<K, V> m,
		                 Class<K> keyType, Class<V> valueType) {
			super(m, keyType, valueType);
			sm = m;
		}

		public Comparator<? super K> comparator() { return sm.comparator(); }
		public K firstKey()                       { return sm.firstKey(); }
		public K lastKey()                        { return sm.lastKey(); }

		public SortedMap<K,V> subMap(K fromKey, K toKey) {
			return checkedSortedMap(sm.subMap(fromKey, toKey),
					keyType, valueType);
		}
		public SortedMap<K,V> headMap(K toKey) {
			return checkedSortedMap(sm.headMap(toKey), keyType, valueType);
		}
		public SortedMap<K,V> tailMap(K fromKey) {
			return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType);
		}
	}

	/**
	 * Returns a dynamically typesafe view of the specified navigable map.
	 * Any attempt to insert a mapping whose key or value have the wrong
	 * type will result in an immediate {@link ClassCastException}.
	 * Similarly, any attempt to modify the value currently associated with
	 * a key will result in an immediate {@link ClassCastException},
	 * whether the modification is attempted directly through the map
	 * itself, or through a {@link Map.Entry} instance obtained from the
	 * map's {@link Map#entrySet() entry set} view.
	 *
	 * <p>Assuming a map contains no incorrectly typed keys or values
	 * prior to the time a dynamically typesafe view is generated, and
	 * that all subsequent access to the map takes place through the view
	 * (or one of its collection views), it is <em>guaranteed</em> that the
	 * map cannot contain an incorrectly typed key or value.
	 *
	 * <p>A discussion of the use of dynamically typesafe views may be
	 * found in the documentation for the {@link #checkedCollection
	 * checkedCollection} method.
	 *
	 * <p>The returned map will be serializable if the specified map is
	 * serializable.
	 *
	 * <p>Since {@code null} is considered to be a value of any reference
	 * type, the returned map permits insertion of null keys or values
	 * whenever the backing map does.
	 *
	 * @param <K> type of map keys
	 * @param <V> type of map values
	 * @param m the map for which a dynamically typesafe view is to be
	 *          returned
	 * @param keyType the type of key that {@code m} is permitted to hold
	 * @param valueType the type of value that {@code m} is permitted to hold
	 * @return a dynamically typesafe view of the specified map
	 * @since 1.8
	 */
	public static <K,V> NavigableMap<K,V> checkedNavigableMap(NavigableMap<K, V> m,
	                                                          Class<K> keyType,
	                                                          Class<V> valueType) {
		return new CheckedNavigableMap<>(m, keyType, valueType);
	}

	/**
	 * @serial include
	 */
	static class CheckedNavigableMap<K,V> extends CheckedSortedMap<K,V>
			implements NavigableMap<K,V>, Serializable
	{
		private static final long serialVersionUID = -4852462692372534096L;

		private final NavigableMap<K, V> nm;

		CheckedNavigableMap(NavigableMap<K, V> m,
		                    Class<K> keyType, Class<V> valueType) {
			super(m, keyType, valueType);
			nm = m;
		}

		public Comparator<? super K> comparator()   { return nm.comparator(); }
		public K firstKey()                           { return nm.firstKey(); }
		public K lastKey()                             { return nm.lastKey(); }

		public Entry<K, V> lowerEntry(K key) {
			Entry<K,V> lower = nm.lowerEntry(key);
			return (null != lower)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType)
					: null;
		}

		public K lowerKey(K key)                   { return nm.lowerKey(key); }

		public Entry<K, V> floorEntry(K key) {
			Entry<K,V> floor = nm.floorEntry(key);
			return (null != floor)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType)
					: null;
		}

		public K floorKey(K key)                   { return nm.floorKey(key); }

		public Entry<K, V> ceilingEntry(K key) {
			Entry<K,V> ceiling = nm.ceilingEntry(key);
			return (null != ceiling)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType)
					: null;
		}

		public K ceilingKey(K key)               { return nm.ceilingKey(key); }

		public Entry<K, V> higherEntry(K key) {
			Entry<K,V> higher = nm.higherEntry(key);
			return (null != higher)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType)
					: null;
		}

		public K higherKey(K key)                 { return nm.higherKey(key); }

		public Entry<K, V> firstEntry() {
			Entry<K,V> first = nm.firstEntry();
			return (null != first)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType)
					: null;
		}

		public Entry<K, V> lastEntry() {
			Entry<K,V> last = nm.lastEntry();
			return (null != last)
					? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType)
					: null;
		}

		public Entry<K, V> pollFirstEntry() {
			Entry<K,V> entry = nm.pollFirstEntry();
			return (null == entry)
					? null
					: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
		}

		public Entry<K, V> pollLastEntry() {
			Entry<K,V> entry = nm.pollLastEntry();
			return (null == entry)
					? null
					: new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType);
		}

		public NavigableMap<K, V> descendingMap() {
			return checkedNavigableMap(nm.descendingMap(), keyType, valueType);
		}

		public NavigableSet<K> keySet() {
			return navigableKeySet();
		}

		public NavigableSet<K> navigableKeySet() {
			return checkedNavigableSet(nm.navigableKeySet(), keyType);
		}

		public NavigableSet<K> descendingKeySet() {
			return checkedNavigableSet(nm.descendingKeySet(), keyType);
		}

		@Override
		public NavigableMap<K,V> subMap(K fromKey, K toKey) {
			return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false),
					keyType, valueType);
		}

		@Override
		public NavigableMap<K,V> headMap(K toKey) {
			return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType);
		}

		@Override
		public NavigableMap<K,V> tailMap(K fromKey) {
			return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType);
		}

		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType);
		}

		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType);
		}

		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType);
		}
	}

	// Empty collections

	/**
	 * Returns an iterator that has no elements.  More precisely,
	 *
	 * <ul>
	 * <li>{@link Iterator#hasNext hasNext} always returns {@code
	 * false}.</li>
	 * <li>{@link Iterator#next next} always throws {@link
	 * NoSuchElementException}.</li>
	 * <li>{@link Iterator#remove remove} always throws {@link
	 * IllegalStateException}.</li>
	 * </ul>
	 *
	 * <p>Implementations of this method are permitted, but not
	 * required, to return the same object from multiple invocations.
	 *
	 * @param <T> type of elements, if there were any, in the iterator
	 * @return an empty iterator
	 * @since 1.7
	 */
	@SuppressWarnings("unchecked")
	public static <T> Iterator<T> emptyIterator() {
		return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR;
	}

	private static class EmptyIterator<E> implements Iterator<E> {
		static final EmptyIterator<Object> EMPTY_ITERATOR
				= new EmptyIterator<>();

		public boolean hasNext() { return false; }
		public E next() { throw new NoSuchElementException(); }
		public void remove() { throw new IllegalStateException(); }
		@Override
		public void forEachRemaining(Consumer<? super E> action) {
			Objects.requireNonNull(action);
		}
	}

	/**
	 * Returns a list iterator that has no elements.  More precisely,
	 *
	 * <ul>
	 * <li>{@link Iterator#hasNext hasNext} and {@link
	 * ListIterator#hasPrevious hasPrevious} always return {@code
	 * false}.</li>
	 * <li>{@link Iterator#next next} and {@link ListIterator#previous
	 * previous} always throw {@link NoSuchElementException}.</li>
	 * <li>{@link Iterator#remove remove} and {@link ListIterator#set
	 * set} always throw {@link IllegalStateException}.</li>
	 * <li>{@link ListIterator#add add} always throws {@link
	 * UnsupportedOperationException}.</li>
	 * <li>{@link ListIterator#nextIndex nextIndex} always returns
	 * {@code 0}.</li>
	 * <li>{@link ListIterator#previousIndex previousIndex} always
	 * returns {@code -1}.</li>
	 * </ul>
	 *
	 * <p>Implementations of this method are permitted, but not
	 * required, to return the same object from multiple invocations.
	 *
	 * @param <T> type of elements, if there were any, in the iterator
	 * @return an empty list iterator
	 * @since 1.7
	 */
	@SuppressWarnings("unchecked")
	public static <T> ListIterator<T> emptyListIterator() {
		return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR;
	}

	private static class EmptyListIterator<E>
			extends EmptyIterator<E>
			implements ListIterator<E>
	{
		static final EmptyListIterator<Object> EMPTY_ITERATOR
				= new EmptyListIterator<>();

		public boolean hasPrevious() { return false; }
		public E previous() { throw new NoSuchElementException(); }
		public int nextIndex()     { return 0; }
		public int previousIndex() { return -1; }
		public void set(E e) { throw new IllegalStateException(); }
		public void add(E e) { throw new UnsupportedOperationException(); }
	}

	/**
	 * Returns an enumeration that has no elements.  More precisely,
	 *
	 * <ul>
	 * <li>{@link Enumeration#hasMoreElements hasMoreElements} always
	 * returns {@code false}.</li>
	 * <li> {@link Enumeration#nextElement nextElement} always throws
	 * {@link NoSuchElementException}.</li>
	 * </ul>
	 *
	 * <p>Implementations of this method are permitted, but not
	 * required, to return the same object from multiple invocations.
	 *
	 * @param  <T> the class of the objects in the enumeration
	 * @return an empty enumeration
	 * @since 1.7
	 */
	@SuppressWarnings("unchecked")
	public static <T> Enumeration<T> emptyEnumeration() {
		return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION;
	}

	private static class EmptyEnumeration<E> implements Enumeration<E> {
		static final EmptyEnumeration<Object> EMPTY_ENUMERATION
				= new EmptyEnumeration<>();

		public boolean hasMoreElements() { return false; }
		public E nextElement() { throw new NoSuchElementException(); }
	}

	/**
	 * The empty set (immutable).  This set is serializable.
	 *
	 * @see #emptySet()
	 */
	@SuppressWarnings("rawtypes")
	public static final Set EMPTY_SET = new EmptySet<>();

	/**
	 * Returns an empty set (immutable).  This set is serializable.
	 * Unlike the like-named field, this method is parameterized.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty set:
	 * <pre>
	 *     Set&lt;String&gt; s = Collections.emptySet();
	 * </pre>
	 * @implNote Implementations of this method need not create a separate
	 * {@code Set} object for each call.  Using this method is likely to have
	 * comparable cost to using the like-named field.  (Unlike this method, the
	 * field does not provide type safety.)
	 *
	 * @param  <T> the class of the objects in the set
	 * @return the empty set
	 *
	 * @see #EMPTY_SET
	 * @since 1.5
	 */
	@SuppressWarnings("unchecked")
	public static final <T> Set<T> emptySet() {
		return (Set<T>) EMPTY_SET;
	}

	/**
	 * @serial include
	 */
	private static class EmptySet<E>
			extends AbstractSet<E>
			implements Serializable
	{
		private static final long serialVersionUID = 1582296315990362920L;

		public Iterator<E> iterator() { return emptyIterator(); }

		public int size() {return 0;}
		public boolean isEmpty() {return true;}

		public boolean contains(Object obj) {return false;}
		public boolean containsAll(Collection<?> c) { return c.isEmpty(); }

		public Object[] toArray() { return new Object[0]; }

		public <T> T[] toArray(T[] a) {
			if (a.length > 0)
				a[0] = null;
			return a;
		}

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			Objects.requireNonNull(action);
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			Objects.requireNonNull(filter);
			return false;
		}
		@Override
		public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }

		// Preserves singleton property
		private Object readResolve() {
			return EMPTY_SET;
		}
	}

	/**
	 * Returns an empty sorted set (immutable).  This set is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty
	 * sorted set:
	 * <pre> {@code
	 *     SortedSet<String> s = Collections.emptySortedSet();
	 * }</pre>
	 *
	 * @implNote Implementations of this method need not create a separate
	 * {@code SortedSet} object for each call.
	 *
	 * @param <E> type of elements, if there were any, in the set
	 * @return the empty sorted set
	 * @since 1.8
	 */
	@SuppressWarnings("unchecked")
	public static <E> SortedSet<E> emptySortedSet() {
		return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
	}

	/**
	 * Returns an empty navigable set (immutable).  This set is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty
	 * navigable set:
	 * <pre> {@code
	 *     NavigableSet<String> s = Collections.emptyNavigableSet();
	 * }</pre>
	 *
	 * @implNote Implementations of this method need not
	 * create a separate {@code NavigableSet} object for each call.
	 *
	 * @param <E> type of elements, if there were any, in the set
	 * @return the empty navigable set
	 * @since 1.8
	 */
	@SuppressWarnings("unchecked")
	public static <E> NavigableSet<E> emptyNavigableSet() {
		return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET;
	}

	/**
	 * The empty list (immutable).  This list is serializable.
	 *
	 * @see #emptyList()
	 */
	@SuppressWarnings("rawtypes")
	public static final List EMPTY_LIST = new EmptyList<>();

	/**
	 * Returns an empty list (immutable).  This list is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty list:
	 * <pre>
	 *     List&lt;String&gt; s = Collections.emptyList();
	 * </pre>
	 *
	 * @implNote
	 * Implementations of this method need not create a separate <tt>List</tt>
	 * object for each call.   Using this method is likely to have comparable
	 * cost to using the like-named field.  (Unlike this method, the field does
	 * not provide type safety.)
	 *
	 * @param <T> type of elements, if there were any, in the list
	 * @return an empty immutable list
	 *
	 * @see #EMPTY_LIST
	 * @since 1.5
	 */
	@SuppressWarnings("unchecked")
	public static final <T> List<T> emptyList() {
		return (List<T>) EMPTY_LIST;
	}

	/**
	 * @serial include
	 */
	private static class EmptyList<E>
			extends AbstractList<E>
			implements RandomAccess, Serializable {
		private static final long serialVersionUID = 8842843931221139166L;

		public Iterator<E> iterator() {
			return emptyIterator();
		}
		public ListIterator<E> listIterator() {
			return emptyListIterator();
		}

		public int size() {return 0;}
		public boolean isEmpty() {return true;}

		public boolean contains(Object obj) {return false;}
		public boolean containsAll(Collection<?> c) { return c.isEmpty(); }

		public Object[] toArray() { return new Object[0]; }

		public <T> T[] toArray(T[] a) {
			if (a.length > 0)
				a[0] = null;
			return a;
		}

		public E get(int index) {
			throw new IndexOutOfBoundsException("Index: "+index);
		}

		public boolean equals(Object o) {
			return (o instanceof List) && ((List<?>)o).isEmpty();
		}

		public int hashCode() { return 1; }

		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			Objects.requireNonNull(filter);
			return false;
		}
		@Override
		public void replaceAll(UnaryOperator<E> operator) {
			Objects.requireNonNull(operator);
		}
		@Override
		public void sort(Comparator<? super E> c) {
		}

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			Objects.requireNonNull(action);
		}

		@Override
		public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }

		// Preserves singleton property
		private Object readResolve() {
			return EMPTY_LIST;
		}
	}

	/**
	 * The empty map (immutable).  This map is serializable.
	 *
	 * @see #emptyMap()
	 * @since 1.3
	 */
	@SuppressWarnings("rawtypes")
	public static final Map EMPTY_MAP = new EmptyMap<>();

	/**
	 * Returns an empty map (immutable).  This map is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty map:
	 * <pre>
	 *     Map&lt;String, Date&gt; s = Collections.emptyMap();
	 * </pre>
	 * @implNote Implementations of this method need not create a separate
	 * {@code Map} object for each call.  Using this method is likely to have
	 * comparable cost to using the like-named field.  (Unlike this method, the
	 * field does not provide type safety.)
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @return an empty map
	 * @see #EMPTY_MAP
	 * @since 1.5
	 */
	@SuppressWarnings("unchecked")
	public static final <K,V> Map<K,V> emptyMap() {
		return (Map<K,V>) EMPTY_MAP;
	}

	/**
	 * Returns an empty sorted map (immutable).  This map is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty map:
	 * <pre> {@code
	 *     SortedMap<String, Date> s = Collections.emptySortedMap();
	 * }</pre>
	 *
	 * @implNote Implementations of this method need not create a separate
	 * {@code SortedMap} object for each call.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @return an empty sorted map
	 * @since 1.8
	 */
	@SuppressWarnings("unchecked")
	public static final <K,V> SortedMap<K,V> emptySortedMap() {
		return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
	}

	/**
	 * Returns an empty navigable map (immutable).  This map is serializable.
	 *
	 * <p>This example illustrates the type-safe way to obtain an empty map:
	 * <pre> {@code
	 *     NavigableMap<String, Date> s = Collections.emptyNavigableMap();
	 * }</pre>
	 *
	 * @implNote Implementations of this method need not create a separate
	 * {@code NavigableMap} object for each call.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @return an empty navigable map
	 * @since 1.8
	 */
	@SuppressWarnings("unchecked")
	public static final <K,V> NavigableMap<K,V> emptyNavigableMap() {
		return (NavigableMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
	}

	/**
	 * @serial include
	 */
	private static class EmptyMap<K,V>
			extends AbstractMap<K,V>
			implements Serializable
	{
		private static final long serialVersionUID = 6428348081105594320L;

		public int size()                          {return 0;}
		public boolean isEmpty()                   {return true;}
		public boolean containsKey(Object key)     {return false;}
		public boolean containsValue(Object value) {return false;}
		public V get(Object key)                   {return null;}
		public Set<K> keySet()                     {return emptySet();}
		public Collection<V> values()              {return emptySet();}
		public Set<Map.Entry<K,V>> entrySet()      {return emptySet();}

		public boolean equals(Object o) {
			return (o instanceof Map) && ((Map<?,?>)o).isEmpty();
		}

		public int hashCode()                      {return 0;}

		// Override default methods in Map
		@Override
		@SuppressWarnings("unchecked")
		public V getOrDefault(Object k, V defaultValue) {
			return defaultValue;
		}

		@Override
		public void forEach(BiConsumer<? super K, ? super V> action) {
			Objects.requireNonNull(action);
		}

		@Override
		public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
			Objects.requireNonNull(function);
		}

		@Override
		public V putIfAbsent(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean remove(Object key, Object value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean replace(K key, V oldValue, V newValue) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V replace(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfAbsent(K key,
		                         Function<? super K, ? extends V> mappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfPresent(K key,
		                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V compute(K key,
		                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V merge(K key, V value,
		               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		// Preserves singleton property
		private Object readResolve() {
			return EMPTY_MAP;
		}
	}

	// Singleton collections

	/**
	 * Returns an immutable set containing only the specified object.
	 * The returned set is serializable.
	 *
	 * @param  <T> the class of the objects in the set
	 * @param o the sole object to be stored in the returned set.
	 * @return an immutable set containing only the specified object.
	 */
	public static <T> Set<T> singleton(T o) {
		return new SingletonSet<>(o);
	}

	static <E> Iterator<E> singletonIterator(final E e) {
		return new Iterator<E>() {
			private boolean hasNext = true;
			public boolean hasNext() {
				return hasNext;
			}
			public E next() {
				if (hasNext) {
					hasNext = false;
					return e;
				}
				throw new NoSuchElementException();
			}
			public void remove() {
				throw new UnsupportedOperationException();
			}
			@Override
			public void forEachRemaining(Consumer<? super E> action) {
				Objects.requireNonNull(action);
				if (hasNext) {
					action.accept(e);
					hasNext = false;
				}
			}
		};
	}

	/**
	 * Creates a {@code Spliterator} with only the specified element
	 *
	 * @param <T> Type of elements
	 * @return A singleton {@code Spliterator}
	 */
	static <T> Spliterator<T> singletonSpliterator(final T element) {
		return new Spliterator<T>() {
			long est = 1;

			@Override
			public Spliterator<T> trySplit() {
				return null;
			}

			@Override
			public boolean tryAdvance(Consumer<? super T> consumer) {
				Objects.requireNonNull(consumer);
				if (est > 0) {
					est--;
					consumer.accept(element);
					return true;
				}
				return false;
			}

			@Override
			public void forEachRemaining(Consumer<? super T> consumer) {
				tryAdvance(consumer);
			}

			@Override
			public long estimateSize() {
				return est;
			}

			@Override
			public int characteristics() {
				int value = (element != null) ? Spliterator.NONNULL : 0;

				return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE |
						Spliterator.DISTINCT | Spliterator.ORDERED;
			}
		};
	}

	/**
	 * @serial include
	 */
	private static class SingletonSet<E>
			extends AbstractSet<E>
			implements Serializable
	{
		private static final long serialVersionUID = 3193687207550431679L;

		private final E element;

		SingletonSet(E e) {element = e;}

		public Iterator<E> iterator() {
			return singletonIterator(element);
		}

		public int size() {return 1;}

		public boolean contains(Object o) {return eq(o, element);}

		// Override default methods for Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			action.accept(element);
		}
		@Override
		public Spliterator<E> spliterator() {
			return singletonSpliterator(element);
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			throw new UnsupportedOperationException();
		}
	}

	/**
	 * Returns an immutable list containing only the specified object.
	 * The returned list is serializable.
	 *
	 * @param  <T> the class of the objects in the list
	 * @param o the sole object to be stored in the returned list.
	 * @return an immutable list containing only the specified object.
	 * @since 1.3
	 */
	public static <T> List<T> singletonList(T o) {
		return new SingletonList<>(o);
	}

	/**
	 * @serial include
	 */
	private static class SingletonList<E>
			extends AbstractList<E>
			implements RandomAccess, Serializable {

		private static final long serialVersionUID = 3093736618740652951L;

		private final E element;

		SingletonList(E obj)                {element = obj;}

		public Iterator<E> iterator() {
			return singletonIterator(element);
		}

		public int size()                   {return 1;}

		public boolean contains(Object obj) {return eq(obj, element);}

		public E get(int index) {
			if (index != 0)
				throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
			return element;
		}

		// Override default methods for Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			action.accept(element);
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			throw new UnsupportedOperationException();
		}
		@Override
		public void replaceAll(UnaryOperator<E> operator) {
			throw new UnsupportedOperationException();
		}
		@Override
		public void sort(Comparator<? super E> c) {
		}
		@Override
		public Spliterator<E> spliterator() {
			return singletonSpliterator(element);
		}
	}

	/**
	 * Returns an immutable map, mapping only the specified key to the
	 * specified value.  The returned map is serializable.
	 *
	 * @param <K> the class of the map keys
	 * @param <V> the class of the map values
	 * @param key the sole key to be stored in the returned map.
	 * @param value the value to which the returned map maps <tt>key</tt>.
	 * @return an immutable map containing only the specified key-value
	 *         mapping.
	 * @since 1.3
	 */
	public static <K,V> Map<K,V> singletonMap(K key, V value) {
		return new SingletonMap<>(key, value);
	}

	/**
	 * @serial include
	 */
	private static class SingletonMap<K,V>
			extends AbstractMap<K,V>
			implements Serializable {
		private static final long serialVersionUID = -6979724477215052911L;

		private final K k;
		private final V v;

		SingletonMap(K key, V value) {
			k = key;
			v = value;
		}

		public int size()                                           {return 1;}
		public boolean isEmpty()                                {return false;}
		public boolean containsKey(Object key)             {return eq(key, k);}
		public boolean containsValue(Object value)       {return eq(value, v);}
		public V get(Object key)              {return (eq(key, k) ? v : null);}

		private transient Set<K> keySet;
		private transient Set<Map.Entry<K,V>> entrySet;
		private transient Collection<V> values;

		public Set<K> keySet() {
			if (keySet==null)
				keySet = singleton(k);
			return keySet;
		}

		public Set<Map.Entry<K,V>> entrySet() {
			if (entrySet==null)
				entrySet = Collections.<Map.Entry<K,V>>singleton(
						new SimpleImmutableEntry<>(k, v));
			return entrySet;
		}

		public Collection<V> values() {
			if (values==null)
				values = singleton(v);
			return values;
		}

		// Override default methods in Map
		@Override
		public V getOrDefault(Object key, V defaultValue) {
			return eq(key, k) ? v : defaultValue;
		}

		@Override
		public void forEach(BiConsumer<? super K, ? super V> action) {
			action.accept(k, v);
		}

		@Override
		public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V putIfAbsent(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean remove(Object key, Object value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean replace(K key, V oldValue, V newValue) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V replace(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfAbsent(K key,
		                         Function<? super K, ? extends V> mappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V computeIfPresent(K key,
		                          BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V compute(K key,
		                 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V merge(K key, V value,
		               BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
			throw new UnsupportedOperationException();
		}
	}

	// Miscellaneous

	/**
	 * Returns an immutable list consisting of <tt>n</tt> copies of the
	 * specified object.  The newly allocated data object is tiny (it contains
	 * a single reference to the data object).  This method is useful in
	 * combination with the <tt>List.addAll</tt> method to grow lists.
	 * The returned list is serializable.
	 *
	 * @param  <T> the class of the object to copy and of the objects
	 *         in the returned list.
	 * @param  n the number of elements in the returned list.
	 * @param  o the element to appear repeatedly in the returned list.
	 * @return an immutable list consisting of <tt>n</tt> copies of the
	 *         specified object.
	 * @throws IllegalArgumentException if {@code n < 0}
	 * @see    List#addAll(Collection)
	 * @see    List#addAll(int, Collection)
	 */
	public static <T> List<T> nCopies(int n, T o) {
		if (n < 0)
			throw new IllegalArgumentException("List length = " + n);
		return new CopiesList<>(n, o);
	}

	/**
	 * @serial include
	 */
	private static class CopiesList<E>
			extends AbstractList<E>
			implements RandomAccess, Serializable
	{
		private static final long serialVersionUID = 2739099268398711800L;

		final int n;
		final E element;

		CopiesList(int n, E e) {
			assert n >= 0;
			this.n = n;
			element = e;
		}

		public int size() {
			return n;
		}

		public boolean contains(Object obj) {
			return n != 0 && eq(obj, element);
		}

		public int indexOf(Object o) {
			return contains(o) ? 0 : -1;
		}

		public int lastIndexOf(Object o) {
			return contains(o) ? n - 1 : -1;
		}

		public E get(int index) {
			if (index < 0 || index >= n)
				throw new IndexOutOfBoundsException("Index: "+index+
						", Size: "+n);
			return element;
		}

		public Object[] toArray() {
			final Object[] a = new Object[n];
			if (element != null)
				Arrays.fill(a, 0, n, element);
			return a;
		}

		@SuppressWarnings("unchecked")
		public <T> T[] toArray(T[] a) {
			final int n = this.n;
			if (a.length < n) {
				a = (T[])java.lang.reflect.Array
						.newInstance(a.getClass().getComponentType(), n);
				if (element != null)
					Arrays.fill(a, 0, n, element);
			} else {
				Arrays.fill(a, 0, n, element);
				if (a.length > n)
					a[n] = null;
			}
			return a;
		}

		public List<E> subList(int fromIndex, int toIndex) {
			if (fromIndex < 0)
				throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
			if (toIndex > n)
				throw new IndexOutOfBoundsException("toIndex = " + toIndex);
			if (fromIndex > toIndex)
				throw new IllegalArgumentException("fromIndex(" + fromIndex +
						") > toIndex(" + toIndex + ")");
			return new CopiesList<>(toIndex - fromIndex, element);
		}

		// Override default methods in Collection
		@Override
		public Stream<E> stream() {
			return IntStream.range(0, n).mapToObj(i -> element);
		}

		@Override
		public Stream<E> parallelStream() {
			return IntStream.range(0, n).parallel().mapToObj(i -> element);
		}

		@Override
		public Spliterator<E> spliterator() {
			return stream().spliterator();
		}
	}

	/**
	 * Returns a comparator that imposes the reverse of the <em>natural
	 * ordering</em> on a collection of objects that implement the
	 * {@code Comparable} interface.  (The natural ordering is the ordering
	 * imposed by the objects' own {@code compareTo} method.)  This enables a
	 * simple idiom for sorting (or maintaining) collections (or arrays) of
	 * objects that implement the {@code Comparable} interface in
	 * reverse-natural-order.  For example, suppose {@code a} is an array of
	 * strings. Then: <pre>
	 *          Arrays.sort(a, Collections.reverseOrder());
	 * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
	 *
	 * The returned comparator is serializable.
	 *
	 * @param  <T> the class of the objects compared by the comparator
	 * @return A comparator that imposes the reverse of the <i>natural
	 *         ordering</i> on a collection of objects that implement
	 *         the <tt>Comparable</tt> interface.
	 * @see Comparable
	 */
	@SuppressWarnings("unchecked")
	public static <T> Comparator<T> reverseOrder() {
		return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
	}

	/**
	 * @serial include
	 */
	private static class ReverseComparator
			implements Comparator<Comparable<Object>>, Serializable {

		private static final long serialVersionUID = 7207038068494060240L;

		static final ReverseComparator REVERSE_ORDER
				= new ReverseComparator();

		public int compare(Comparable<Object> c1, Comparable<Object> c2) {
			return c2.compareTo(c1);
		}

		private Object readResolve() { return Collections.reverseOrder(); }

		@Override
		public Comparator<Comparable<Object>> reversed() {
			return Comparator.naturalOrder();
		}
	}

	/**
	 * Returns a comparator that imposes the reverse ordering of the specified
	 * comparator.  If the specified comparator is {@code null}, this method is
	 * equivalent to {@link #reverseOrder()} (in other words, it returns a
	 * comparator that imposes the reverse of the <em>natural ordering</em> on
	 * a collection of objects that implement the Comparable interface).
	 *
	 * <p>The returned comparator is serializable (assuming the specified
	 * comparator is also serializable or {@code null}).
	 *
	 * @param <T> the class of the objects compared by the comparator
	 * @param cmp a comparator who's ordering is to be reversed by the returned
	 * comparator or {@code null}
	 * @return A comparator that imposes the reverse ordering of the
	 *         specified comparator.
	 * @since 1.5
	 */
	public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
		if (cmp == null)
			return reverseOrder();

		if (cmp instanceof ReverseComparator2)
			return ((ReverseComparator2<T>)cmp).cmp;

		return new ReverseComparator2<>(cmp);
	}

	/**
	 * @serial include
	 */
	private static class ReverseComparator2<T> implements Comparator<T>,
			Serializable
	{
		private static final long serialVersionUID = 4374092139857L;

		/**
		 * The comparator specified in the static factory.  This will never
		 * be null, as the static factory returns a ReverseComparator
		 * instance if its argument is null.
		 *
		 * @serial
		 */
		final Comparator<T> cmp;

		ReverseComparator2(Comparator<T> cmp) {
			assert cmp != null;
			this.cmp = cmp;
		}

		public int compare(T t1, T t2) {
			return cmp.compare(t2, t1);
		}

		public boolean equals(Object o) {
			return (o == this) ||
					(o instanceof ReverseComparator2 &&
							cmp.equals(((ReverseComparator2)o).cmp));
		}

		public int hashCode() {
			return cmp.hashCode() ^ Integer.MIN_VALUE;
		}

		@Override
		public Comparator<T> reversed() {
			return cmp;
		}
	}

	/**
	 * Returns an enumeration over the specified collection.  This provides
	 * interoperability with legacy APIs that require an enumeration
	 * as input.
	 *
	 * @param  <T> the class of the objects in the collection
	 * @param c the collection for which an enumeration is to be returned.
	 * @return an enumeration over the specified collection.
	 * @see Enumeration
	 */
	public static <T> Enumeration<T> enumeration(final Collection<T> c) {
		return new Enumeration<T>() {
			private final Iterator<T> i = c.iterator();

			public boolean hasMoreElements() {
				return i.hasNext();
			}

			public T nextElement() {
				return i.next();
			}
		};
	}

	/**
	 * Returns an array list containing the elements returned by the
	 * specified enumeration in the order they are returned by the
	 * enumeration.  This method provides interoperability between
	 * legacy APIs that return enumerations and new APIs that require
	 * collections.
	 *
	 * @param <T> the class of the objects returned by the enumeration
	 * @param e enumeration providing elements for the returned
	 *          array list
	 * @return an array list containing the elements returned
	 *         by the specified enumeration.
	 * @since 1.4
	 * @see Enumeration
	 * @see ArrayList
	 */
	public static <T> ArrayList<T> list(Enumeration<T> e) {
		ArrayList<T> l = new ArrayList<>();
		while (e.hasMoreElements())
			l.add(e.nextElement());
		return l;
	}

	/**
	 * Returns true if the specified arguments are equal, or both null.
	 *
	 * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
	 */
	static boolean eq(Object o1, Object o2) {
		return o1==null ? o2==null : o1.equals(o2);
	}

	/**
	 * Returns the number of elements in the specified collection equal to the
	 * specified object.  More formally, returns the number of elements
	 * <tt>e</tt> in the collection such that
	 * <tt>(o == null ? e == null : o.equals(e))</tt>.
	 *
	 * @param c the collection in which to determine the frequency
	 *     of <tt>o</tt>
	 * @param o the object whose frequency is to be determined
	 * @return the number of elements in {@code c} equal to {@code o}
	 * @throws NullPointerException if <tt>c</tt> is null
	 * @since 1.5
	 */
	public static int frequency(Collection<?> c, Object o) {
		int result = 0;
		if (o == null) {
			for (Object e : c)
				if (e == null)
					result++;
		} else {
			for (Object e : c)
				if (o.equals(e))
					result++;
		}
		return result;
	}

	/**
	 * Returns {@code true} if the two specified collections have no
	 * elements in common.
	 *
	 * <p>Care must be exercised if this method is used on collections that
	 * do not comply with the general contract for {@code Collection}.
	 * Implementations may elect to iterate over either collection and test
	 * for containment in the other collection (or to perform any equivalent
	 * computation).  If either collection uses a nonstandard equality test
	 * (as does a {@link SortedSet} whose ordering is not <em>compatible with
	 * equals</em>, or the key set of an {@link IdentityHashMap}), both
	 * collections must use the same nonstandard equality test, or the
	 * result of this method is undefined.
	 *
	 * <p>Care must also be exercised when using collections that have
	 * restrictions on the elements that they may contain. Collection
	 * implementations are allowed to throw exceptions for any operation
	 * involving elements they deem ineligible. For absolute safety the
	 * specified collections should contain only elements which are
	 * eligible elements for both collections.
	 *
	 * <p>Note that it is permissible to pass the same collection in both
	 * parameters, in which case the method will return {@code true} if and
	 * only if the collection is empty.
	 *
	 * @param c1 a collection
	 * @param c2 a collection
	 * @return {@code true} if the two specified collections have no
	 * elements in common.
	 * @throws NullPointerException if either collection is {@code null}.
	 * @throws NullPointerException if one collection contains a {@code null}
	 * element and {@code null} is not an eligible element for the other collection.
	 * (<a href="Collection.html#optional-restrictions">optional</a>)
	 * @throws ClassCastException if one collection contains an element that is
	 * of a type which is ineligible for the other collection.
	 * (<a href="Collection.html#optional-restrictions">optional</a>)
	 * @since 1.5
	 */
	public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
		// The collection to be used for contains(). Preference is given to
		// the collection who's contains() has lower O() complexity.
		Collection<?> contains = c2;
		// The collection to be iterated. If the collections' contains() impl
		// are of different O() complexity, the collection with slower
		// contains() will be used for iteration. For collections who's
		// contains() are of the same complexity then best performance is
		// achieved by iterating the smaller collection.
		Collection<?> iterate = c1;

		// Performance optimization cases. The heuristics:
		//   1. Generally iterate over c1.
		//   2. If c1 is a Set then iterate over c2.
		//   3. If either collection is empty then result is always true.
		//   4. Iterate over the smaller Collection.
		if (c1 instanceof Set) {
			// Use c1 for contains as a Set's contains() is expected to perform
			// better than O(N/2)
			iterate = c2;
			contains = c1;
		} else if (!(c2 instanceof Set)) {
			// Both are mere Collections. Iterate over smaller collection.
			// Example: If c1 contains 3 elements and c2 contains 50 elements and
			// assuming contains() requires ceiling(N/2) comparisons then
			// checking for all c1 elements in c2 would require 75 comparisons
			// (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring
			// 100 comparisons (50 * ceiling(3/2)).
			int c1size = c1.size();
			int c2size = c2.size();
			if (c1size == 0 || c2size == 0) {
				// At least one collection is empty. Nothing will match.
				return true;
			}

			if (c1size > c2size) {
				iterate = c2;
				contains = c1;
			}
		}

		for (Object e : iterate) {
			if (contains.contains(e)) {
				// Found a common element. Collections are not disjoint.
				return false;
			}
		}

		// No common elements were found.
		return true;
	}

	/**
	 * Adds all of the specified elements to the specified collection.
	 * Elements to be added may be specified individually or as an array.
	 * The behavior of this convenience method is identical to that of
	 * <tt>c.addAll(Arrays.asList(elements))</tt>, but this method is likely
	 * to run significantly faster under most implementations.
	 *
	 * <p>When elements are specified individually, this method provides a
	 * convenient way to add a few elements to an existing collection:
	 * <pre>
	 *     Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon");
	 * </pre>
	 *
	 * @param  <T> the class of the elements to add and of the collection
	 * @param c the collection into which <tt>elements</tt> are to be inserted
	 * @param elements the elements to insert into <tt>c</tt>
	 * @return <tt>true</tt> if the collection changed as a result of the call
	 * @throws UnsupportedOperationException if <tt>c</tt> does not support
	 *         the <tt>add</tt> operation
	 * @throws NullPointerException if <tt>elements</tt> contains one or more
	 *         null values and <tt>c</tt> does not permit null elements, or
	 *         if <tt>c</tt> or <tt>elements</tt> are <tt>null</tt>
	 * @throws IllegalArgumentException if some property of a value in
	 *         <tt>elements</tt> prevents it from being added to <tt>c</tt>
	 * @see Collection#addAll(Collection)
	 * @since 1.5
	 */
	@SafeVarargs
	public static <T> boolean addAll(Collection<? super T> c, T... elements) {
		boolean result = false;
		for (T element : elements)
			result |= c.add(element);
		return result;
	}

	/**
	 * Returns a set backed by the specified map.  The resulting set displays
	 * the same ordering, concurrency, and performance characteristics as the
	 * backing map.  In essence, this factory method provides a {@link Set}
	 * implementation corresponding to any {@link Map} implementation.  There
	 * is no need to use this method on a {@link Map} implementation that
	 * already has a corresponding {@link Set} implementation (such as {@link
	 * HashMap} or {@link TreeMap}).
	 *
	 * <p>Each method invocation on the set returned by this method results in
	 * exactly one method invocation on the backing map or its <tt>keySet</tt>
	 * view, with one exception.  The <tt>addAll</tt> method is implemented
	 * as a sequence of <tt>put</tt> invocations on the backing map.
	 *
	 * <p>The specified map must be empty at the time this method is invoked,
	 * and should not be accessed directly after this method returns.  These
	 * conditions are ensured if the map is created empty, passed directly
	 * to this method, and no reference to the map is retained, as illustrated
	 * in the following code fragment:
	 * <pre>
	 *    Set&lt;Object&gt; weakHashSet = Collections.newSetFromMap(
	 *        new WeakHashMap&lt;Object, Boolean&gt;());
	 * </pre>
	 *
	 * @param <E> the class of the map keys and of the objects in the
	 *        returned set
	 * @param map the backing map
	 * @return the set backed by the map
	 * @throws IllegalArgumentException if <tt>map</tt> is not empty
	 * @since 1.6
	 */
	public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
		return new SetFromMap<>(map);
	}

	/**
	 * @serial include
	 */
	private static class SetFromMap<E> extends AbstractSet<E>
			implements Set<E>, Serializable
	{
		private final Map<E, Boolean> m;  // The backing map
		private transient Set<E> s;       // Its keySet

		SetFromMap(Map<E, Boolean> map) {
			if (!map.isEmpty())
				throw new IllegalArgumentException("Map is non-empty");
			m = map;
			s = map.keySet();
		}

		public void clear()               {        m.clear(); }
		public int size()                 { return m.size(); }
		public boolean isEmpty()          { return m.isEmpty(); }
		public boolean contains(Object o) { return m.containsKey(o); }
		public boolean remove(Object o)   { return m.remove(o) != null; }
		public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
		public Iterator<E> iterator()     { return s.iterator(); }
		public Object[] toArray()         { return s.toArray(); }
		public <T> T[] toArray(T[] a)     { return s.toArray(a); }
		public String toString()          { return s.toString(); }
		public int hashCode()             { return s.hashCode(); }
		public boolean equals(Object o)   { return o == this || s.equals(o); }
		public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
		public boolean removeAll(Collection<?> c)   {return s.removeAll(c);}
		public boolean retainAll(Collection<?> c)   {return s.retainAll(c);}
		// addAll is the only inherited implementation

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {
			s.forEach(action);
		}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			return s.removeIf(filter);
		}

		@Override
		public Spliterator<E> spliterator() {return s.spliterator();}
		@Override
		public Stream<E> stream()           {return s.stream();}
		@Override
		public Stream<E> parallelStream()   {return s.parallelStream();}

		private static final long serialVersionUID = 2454657854757543876L;

		private void readObject(java.io.ObjectInputStream stream)
				throws IOException, ClassNotFoundException
		{
			stream.defaultReadObject();
			s = m.keySet();
		}
	}

	/**
	 * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo)
	 * {@link Queue}. Method <tt>add</tt> is mapped to <tt>push</tt>,
	 * <tt>remove</tt> is mapped to <tt>pop</tt> and so on. This
	 * view can be useful when you would like to use a method
	 * requiring a <tt>Queue</tt> but you need Lifo ordering.
	 *
	 * <p>Each method invocation on the queue returned by this method
	 * results in exactly one method invocation on the backing deque, with
	 * one exception.  The {@link Queue#addAll addAll} method is
	 * implemented as a sequence of {@link Deque#addFirst addFirst}
	 * invocations on the backing deque.
	 *
	 * @param  <T> the class of the objects in the deque
	 * @param deque the deque
	 * @return the queue
	 * @since  1.6
	 */
	public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
		return new AsLIFOQueue<>(deque);
	}

	/**
	 * @serial include
	 */
	static class AsLIFOQueue<E> extends AbstractQueue<E>
			implements Queue<E>, Serializable {
		private static final long serialVersionUID = 1802017725587941708L;
		private final Deque<E> q;
		AsLIFOQueue(Deque<E> q)           { this.q = q; }
		public boolean add(E e)           { q.addFirst(e); return true; }
		public boolean offer(E e)         { return q.offerFirst(e); }
		public E poll()                   { return q.pollFirst(); }
		public E remove()                 { return q.removeFirst(); }
		public E peek()                   { return q.peekFirst(); }
		public E element()                { return q.getFirst(); }
		public void clear()               {        q.clear(); }
		public int size()                 { return q.size(); }
		public boolean isEmpty()          { return q.isEmpty(); }
		public boolean contains(Object o) { return q.contains(o); }
		public boolean remove(Object o)   { return q.remove(o); }
		public Iterator<E> iterator()     { return q.iterator(); }
		public Object[] toArray()         { return q.toArray(); }
		public <T> T[] toArray(T[] a)     { return q.toArray(a); }
		public String toString()          { return q.toString(); }
		public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
		public boolean removeAll(Collection<?> c)   {return q.removeAll(c);}
		public boolean retainAll(Collection<?> c)   {return q.retainAll(c);}
		// We use inherited addAll; forwarding addAll would be wrong

		// Override default methods in Collection
		@Override
		public void forEach(Consumer<? super E> action) {q.forEach(action);}
		@Override
		public boolean removeIf(Predicate<? super E> filter) {
			return q.removeIf(filter);
		}
		@Override
		public Spliterator<E> spliterator() {return q.spliterator();}
		@Override
		public Stream<E> stream()           {return q.stream();}
		@Override
		public Stream<E> parallelStream()   {return q.parallelStream();}
	}
}
